Support 50Hz(PAL) (#648) (PR #658)

- Added Configuration GUI to include checkbox for "50Hz" - Implicitly use PAL or NTSC base 6502 clocks depending on video refresh rate - Added new -50hz and -60hz command line switches - Updated save-state for video refresh rate 1.28.8.0: Updated version & history.txt
2024-12-23 00:30:17 +00:00 · 2019-06-28 21:34:34 +01:00 · 2019-06-28 21:34:34 +01:00 · bd86088c59
commit bd86088c59
parent dbcb789442
19 changed files with 251 additions and 83 deletions
--- a/AppleWinExpress2015.vcxproj
+++ b/AppleWinExpress2015.vcxproj
@ -369,6 +369,7 @@
      <SDLCheck>true</SDLCheck>
      <AdditionalIncludeDirectories>source\cpu;source\emulator;source\debugger;zlib;zip_lib;libyaml\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
      <RuntimeLibrary>MultiThreadedDebug</RuntimeLibrary>
+      <BasicRuntimeChecks>Default</BasicRuntimeChecks>
    </ClCompile>
    <Link>
      <SubSystem>Windows</SubSystem>
--- a/bin/History.txt
+++ b/bin/History.txt
@ -8,10 +8,17 @@ https://github.com/AppleWin/AppleWin/issues/new

 Tom Charlesworth

+1.28.8.0 - 28 Jun 2019
+----------------------
+. [Change #648] Support 50Hz(PAL) video refresh rate and implicitly PAL 1.018MHz.
+	- NB. TV video modes still use NTSC rendering.
+. [Bug #656] Fix for PAGE1/2 ($C054/55) not having a 1 cycle delay.
+
+
 1.28.7.0 - 15 Jun 2019
 ----------------------
 . [Bug #654] Fix for Sather's "Little Text Window" not rendering correctly.
-. [Bug #654] Fix for 6522 TIMER1's period to be N+2 cycles.
+. [Bug #652] Fix for 6522 TIMER1's period to be N+2 cycles.


 1.28.6.0 - 2 Jun 2019
--- a/resource/Applewin.rc
+++ b/resource/Applewin.rc
@ -111,6 +111,7 @@ BEGIN
    CTEXT           "2.0",IDC_2_0_MHz,96,180,20,10
    RTEXT           "Fastest",IDC_MAX_MHz,150,180,29,10
    PUSHBUTTON      "&Benchmark Emulator",IDC_BENCHMARK,15,194,85,15
+    CONTROL         "50Hz video",IDC_CHECK_50HZ_VIDEO,"Button",BS_AUTOCHECKBOX | WS_TABSTOP,142,141,51,10
 END

 IDD_PROPPAGE_INPUT DIALOGEX 0, 0, 210, 215
--- a/resource/resource.h
+++ b/resource/resource.h
@ -116,6 +116,7 @@
 #define IDC_COMBO_DISK2                 1081
 #define IDC_CHECK_FS_SHOW_SUBUNIT_STATUS 1082
 #define IDC_CHECK_VERTICAL_BLEND        1083
+#define IDC_CHECK_50HZ_VIDEO            1084
 #define IDM_EXIT                        40001
 #define IDM_HELP                        40002
 #define IDM_ABOUT                       40003
--- a/resource/version.h
+++ b/resource/version.h
@ -1,4 +1,4 @@
-#define APPLEWIN_VERSION 1,28,7,0
+#define APPLEWIN_VERSION 1,28,8,0

 #define xstr(a) str(a)
 #define str(a) #a
--- a/source/Applewin.cpp
+++ b/source/Applewin.cpp
@ -91,7 +91,7 @@ bool      g_bRestart = false;
 bool      g_bRestartFullScreen = false;

 DWORD		g_dwSpeed		= SPEED_NORMAL;	// Affected by Config dialog's speed slider bar
-double		g_fCurrentCLK6502 = CLK_6502;	// Affected by Config dialog's speed slider bar
+double		g_fCurrentCLK6502 = CLK_6502_NTSC;	// Affected by Config dialog's speed slider bar
 static double g_fMHz		= 1.0;			// Affected by Config dialog's speed slider bar

 int			g_nCpuCyclesFeedback = 0;
@ -345,6 +345,7 @@ static void ContinueExecution(void)

 	//

+	const UINT dwClksPerFrame = NTSC_GetCyclesPerFrame();
 	if (g_dwCyclesThisFrame >= dwClksPerFrame)
 	{
 		g_dwCyclesThisFrame -= dwClksPerFrame;
@ -376,14 +377,21 @@ void SingleStep(bool bReinit)

 //===========================================================================

+double Get6502BaseClock(void)
+{
+	return (GetVideoRefreshRate() == VR_50HZ) ? CLK_6502_PAL : CLK_6502_NTSC;
+}
+
 void SetCurrentCLK6502(void)
 {
 	static DWORD dwPrevSpeed = (DWORD) -1;
+	static VideoRefreshRate_e prevVideoRefreshRate = VR_NONE;

-	if(dwPrevSpeed == g_dwSpeed)
+	if (dwPrevSpeed == g_dwSpeed && GetVideoRefreshRate() == prevVideoRefreshRate)
 		return;

 	dwPrevSpeed = g_dwSpeed;
+	prevVideoRefreshRate = GetVideoRefreshRate();

 	// SPEED_MIN    =  0 = 0.50 MHz
 	// SPEED_NORMAL = 10 = 1.00 MHz
@ -396,7 +404,7 @@ void SetCurrentCLK6502(void)
 	else
 		g_fMHz = (double)g_dwSpeed / 10.0;

-	g_fCurrentCLK6502 = CLK_6502 * g_fMHz;
+	g_fCurrentCLK6502 = Get6502BaseClock() * g_fMHz;

 	//
 	// Now re-init modules that are dependent on /g_fCurrentCLK6502/
@ -622,17 +630,15 @@ void LoadConfiguration(void)
 	}

 	REGLOAD(TEXT(REGVALUE_EMULATION_SPEED)   ,&g_dwSpeed);
+	Config_Load_Video();
+	SetCurrentCLK6502();	// Pre: g_dwSpeed && Config_Load_Video()->SetVideoRefreshRate()

 	DWORD dwEnhanceDisk;
 	REGLOAD(TEXT(REGVALUE_ENHANCE_DISK_SPEED), &dwEnhanceDisk);
 	sg_Disk2Card.SetEnhanceDisk(dwEnhanceDisk ? true : false);

-	Config_Load_Video();
-
 	REGLOAD(TEXT("Uthernet Active")   ,(DWORD *)&tfe_enabled);

-	SetCurrentCLK6502();
-
 	//

 	DWORD dwTmp;
@ -1181,6 +1187,7 @@ int APIENTRY WinMain(HINSTANCE passinstance, HINSTANCE, LPSTR lpCmdLine, int)
 	int newVideoType = -1;
 	int newVideoStyleEnableMask = 0;
 	int newVideoStyleDisableMask = 0;
+	VideoRefreshRate_e newVideoRefreshRate = VR_NONE;
 	LPSTR szScreenshotFilename = NULL;

 	while (*lpCmdLine)
@ -1427,6 +1434,14 @@ int APIENTRY WinMain(HINSTANCE passinstance, HINSTANCE, LPSTR lpCmdLine, int)
 			szScreenshotFilename = GetCurrArg(lpNextArg);
 			lpNextArg = GetNextArg(lpNextArg);
 		}
+		else if (_stricmp(lpCmdLine, "-50hz") == 0)	// (case-insensitive)
+		{
+			newVideoRefreshRate = VR_50HZ;
+		}
+		else if (_stricmp(lpCmdLine, "-60hz") == 0)	// (case-insensitive)
+		{
+			newVideoRefreshRate = VR_60HZ;
+		}
 		else	// unsupported
 		{
 			LogFileOutput("Unsupported arg: %s\n", lpCmdLine);
@ -1537,9 +1552,19 @@ int APIENTRY WinMain(HINSTANCE passinstance, HINSTANCE, LPSTR lpCmdLine, int)
 		LogFileOutput("Main: LoadConfiguration()\n");

 		if (newVideoType >= 0)
+		{
 			SetVideoType( (VideoType_e)newVideoType );
+			newVideoType = -1;	// Don't reapply after a restart
+		}
 		SetVideoStyle( (VideoStyle_e) ((GetVideoStyle() | newVideoStyleEnableMask) & ~newVideoStyleDisableMask) );

+		if (newVideoRefreshRate != VR_NONE)
+		{
+			SetVideoRefreshRate(newVideoRefreshRate);
+			newVideoRefreshRate = VR_NONE;	// Don't reapply after a restart
+			SetCurrentCLK6502();
+		}
+
 		// Apply the memory expansion switches after loading the Apple II machine type
 #ifdef RAMWORKS
 		if (uRamWorksExPages)
--- a/source/Applewin.h
+++ b/source/Applewin.h
@ -6,7 +6,6 @@
 void LogFileTimeUntilFirstKeyReadReset(void);
 void LogFileTimeUntilFirstKeyRead(void);

-void SetCurrentCLK6502();
 bool SetCurrentImageDir(const char* pszImageDir);

 extern const UINT16* GetOldAppleWinVersion(void);
@ -18,6 +17,9 @@ extern eApple2Type g_Apple2Type;
 eApple2Type GetApple2Type(void);
 void SetApple2Type(eApple2Type type);

+double Get6502BaseClock(void);
+void SetCurrentCLK6502(void);
+
 void SingleStep(bool bReinit);

 extern bool       g_bFullSpeed;
--- a/source/Common.h
+++ b/source/Common.h
@ -1,19 +1,11 @@
 #pragma once

-const double _M14 = (157500000.0 / 11.0); // 14.3181818... * 10^6
-const double CLK_6502 = ((_M14 * 65.0) / 912.0); // 65 cycles per 912 14M clocks
+const double _14M_NTSC = (157500000.0 / 11.0);	// 14.3181818... * 10^6
+const double _14M_PAL = 14.25045e6;				// UTAIIe:3-17
+const double CLK_6502_NTSC = ((_14M_NTSC * 65.0) / 912.0); // 65 cycles per 912 14M clocks
+const double CLK_6502_PAL = _14M_PAL / 14.0;
 //const double CLK_6502 = 23 * 44100;			// 1014300

-// The effective Z-80 clock rate is 2.041MHz
-// See: http://www.apple2info.net/hardware/softcard/SC-SWHW_a2in.pdf
-const double CLK_Z80 = (CLK_6502 * 2);
-
-// TODO: Clean up from Common.h, Video.cpp, and NTSC.h !!!
-const UINT uCyclesPerLine			= 65;	// 25 cycles of HBL & 40 cycles of HBL'
-const UINT uVisibleLinesPerFrame	= 64*3;	// 192
-const UINT uLinesPerFrame			= 262;	// 64 in each third of the screen & 70 in VBL
-const DWORD dwClksPerFrame			= uCyclesPerLine * uLinesPerFrame;	// 17030
-
 #define NUM_SLOTS 8

 #define  MAX(a,b)          (((a) > (b)) ? (a) : (b))
@ -107,6 +99,7 @@ enum AppMode_e
 #define  REGVALUE_VIDEO_STYLE         "Video Style"			// GH#616: Added at 1.28.2
 #define  REGVALUE_VIDEO_HALF_SCAN_LINES "Half Scan Lines"	// GH#616: Deprecated from 1.28.2
 #define  REGVALUE_VIDEO_MONO_COLOR      "Monochrome Color"
+#define  REGVALUE_VIDEO_REFRESH_RATE    "Video Refresh Rate"
 #define  REGVALUE_SERIAL_PORT_NAME   "Serial Port Name"
 #define  REGVALUE_ENHANCE_DISK_SPEED "Enhance Disk Speed"
 #define  REGVALUE_CUSTOM_SPEED       "Custom Speed"
--- a/source/Configuration/Config.h
+++ b/source/Configuration/Config.h
@ -4,6 +4,7 @@
 #include "../CPU.h"
 #include "../DiskImage.h"	// Disk_Status_e
 #include "../Harddisk.h"	// HD_CardIsEnabled()
+#include "../Video.h"		// VideoRefreshRate_e, GetVideoRefreshRate()

 class CConfigNeedingRestart
 {
@ -11,7 +12,8 @@ public:
 	CConfigNeedingRestart(UINT bEnableTheFreezesF8Rom = false) :
 		m_Apple2Type( GetApple2Type() ),
 		m_CpuType( GetMainCpu() ),
-		m_uSaveLoadStateMsg(0)
+		m_uSaveLoadStateMsg(0),
+		m_videoRefreshRate( GetVideoRefreshRate() )
 	{
 		m_bEnableHDD = HD_CardIsEnabled();
 		m_bEnableTheFreezesF8Rom = bEnableTheFreezesF8Rom;
@ -29,17 +31,19 @@ public:
 		m_bEnableHDD = other.m_bEnableHDD;
 		m_bEnableTheFreezesF8Rom = other.m_bEnableTheFreezesF8Rom;
 		m_uSaveLoadStateMsg = other.m_uSaveLoadStateMsg;
+		m_videoRefreshRate = other.m_videoRefreshRate;
 		return *this;
 	}

 	bool operator== (const CConfigNeedingRestart& other) const
 	{
 		return	m_Apple2Type == other.m_Apple2Type &&
-				m_CpuType == other.m_CpuType &&
-				memcmp(m_Slot, other.m_Slot, sizeof(m_Slot)) == 0 &&
-				m_bEnableHDD == other.m_bEnableHDD &&
-				m_bEnableTheFreezesF8Rom == other.m_bEnableTheFreezesF8Rom &&
-				m_uSaveLoadStateMsg == other.m_uSaveLoadStateMsg;
+			m_CpuType == other.m_CpuType &&
+			memcmp(m_Slot, other.m_Slot, sizeof(m_Slot)) == 0 &&
+			m_bEnableHDD == other.m_bEnableHDD &&
+			m_bEnableTheFreezesF8Rom == other.m_bEnableTheFreezesF8Rom &&
+			m_uSaveLoadStateMsg == other.m_uSaveLoadStateMsg &&
+			m_videoRefreshRate == other.m_videoRefreshRate;
 	}

 	bool operator!= (const CConfigNeedingRestart& other) const
@ -54,4 +58,5 @@ public:
 	bool m_bEnableHDD;
 	UINT m_bEnableTheFreezesF8Rom;
 	UINT m_uSaveLoadStateMsg;
+	VideoRefreshRate_e m_videoRefreshRate;
 };
--- a/source/Configuration/PageConfig.cpp
+++ b/source/Configuration/PageConfig.cpp
@ -121,6 +121,7 @@ BOOL CPageConfig::DlgProcInternal(HWND hWnd, UINT message, WPARAM wparam, LPARAM
 		case IDC_CHECK_HALF_SCAN_LINES:
 		case IDC_CHECK_VERTICAL_BLEND:
 		case IDC_CHECK_FS_SHOW_SUBUNIT_STATUS:
+		case IDC_CHECK_50HZ_VIDEO:
 			// Checked in DlgOK()
 			break;

@ -205,6 +206,8 @@ BOOL CPageConfig::DlgProcInternal(HWND hWnd, UINT message, WPARAM wparam, LPARAM
 			m_PropertySheetHelper.FillComboBox(hWnd,IDC_SERIALPORT, sg_SSC.GetSerialPortChoices(), sg_SSC.GetSerialPort());
 			EnableWindow(GetDlgItem(hWnd, IDC_SERIALPORT), !sg_SSC.IsActive() ? TRUE : FALSE);

+			CheckDlgButton(hWnd, IDC_CHECK_50HZ_VIDEO, (GetVideoRefreshRate() == VR_50HZ) ? BST_CHECKED : BST_UNCHECKED);
+
 			SendDlgItemMessage(hWnd,IDC_SLIDER_CPU_SPEED,TBM_SETRANGE,1,MAKELONG(0,40));
 			SendDlgItemMessage(hWnd,IDC_SLIDER_CPU_SPEED,TBM_SETPAGESIZE,0,5);
 			SendDlgItemMessage(hWnd,IDC_SLIDER_CPU_SPEED,TBM_SETTICFREQ,10,0);
@ -286,6 +289,13 @@ void CPageConfig::DlgOK(HWND hWnd)
 		bVideoReinit = true;
 	}

+	const bool isNewVideoRate50Hz = IsDlgButtonChecked(hWnd, IDC_CHECK_50HZ_VIDEO) != 0;
+	const bool isCurrentVideoRate50Hz = GetVideoRefreshRate() == VR_50HZ;
+	if (isCurrentVideoRate50Hz != isNewVideoRate50Hz)
+	{
+		m_PropertySheetHelper.GetConfigNew().m_videoRefreshRate = isNewVideoRate50Hz ? VR_50HZ : VR_60HZ;
+	}
+
 	if (bVideoReinit)
 	{
 		Config_Save_Video();
--- a/source/Configuration/PropertySheetHelper.cpp
+++ b/source/Configuration/PropertySheetHelper.cpp
@ -407,6 +407,11 @@ void CPropertySheetHelper::ApplyNewConfig(const CConfigNeedingRestart& ConfigNew
 	{
 		REGSAVE(TEXT(REGVALUE_THE_FREEZES_F8_ROM), ConfigNew.m_bEnableTheFreezesF8Rom);
 	}
+
+	if (CONFIG_CHANGED_LOCAL(m_videoRefreshRate))
+	{
+		REGSAVE(TEXT(REGVALUE_VIDEO_REFRESH_RATE), ConfigNew.m_videoRefreshRate);
+	}
 }

 void CPropertySheetHelper::ApplyNewConfig(void)
@ -423,6 +428,7 @@ void CPropertySheetHelper::SaveCurrentConfig(void)
 	m_ConfigOld.m_Slot[5] = g_Slot5;
 	m_ConfigOld.m_bEnableHDD = HD_CardIsEnabled();
 	m_ConfigOld.m_bEnableTheFreezesF8Rom = sg_PropertySheet.GetTheFreezesF8Rom();
+	m_ConfigOld.m_videoRefreshRate = GetVideoRefreshRate();

 	// Reset flags each time:
 	m_ConfigOld.m_uSaveLoadStateMsg = 0;
@ -441,6 +447,7 @@ void CPropertySheetHelper::RestoreCurrentConfig(void)
 	g_Slot5 = m_ConfigOld.m_Slot[5];
 	HD_SetEnabled(m_ConfigOld.m_bEnableHDD);
 	sg_PropertySheet.SetTheFreezesF8Rom(m_ConfigOld.m_bEnableTheFreezesF8Rom);
+	SetVideoRefreshRate(m_ConfigOld.m_videoRefreshRate);
 }

 bool CPropertySheetHelper::IsOkToSaveLoadState(HWND hWnd, const bool bConfigChanged)
@ -491,6 +498,9 @@ bool CPropertySheetHelper::HardwareConfigChanged(HWND hWnd)
 		if (CONFIG_CHANGED(m_CpuType))
 			strMsgMain += ". Emulated main CPU has changed\n";

+		if (CONFIG_CHANGED(m_videoRefreshRate))
+			strMsgMain += ". Video refresh rate has changed\n";
+
 		if (CONFIG_CHANGED(m_Slot[4]))
 			strMsgMain += GetSlot(4);

--- a/source/Memory.cpp
+++ b/source/Memory.cpp
@ -2202,7 +2202,7 @@ bool MemLoadSnapshot(YamlLoadHelper& yamlLoadHelper, UINT unitVersion)
 			SetLastRamWrite( yamlLoadHelper.LoadUint(SS_YAML_KEY_LASTRAMWRITE) ? TRUE : FALSE );	// NB. This is set later for II,II+ by slot-0 LC or Saturn
 	}

-	if (unitVersion == 3)
+	if (unitVersion >= 3)
 	{
 		for (UINT i=0; i<kNumAnnunciators; i++)
 		{
--- a/source/Mockingboard.cpp
+++ b/source/Mockingboard.cpp
@ -205,7 +205,8 @@ static HANDLE g_hSSI263Event[g_nNumEvents] = {NULL};	// 1: Phoneme finished play
 static DWORD g_dwMaxPhonemeLen = 0;

 // When 6522 IRQ is *not* active use 60Hz update freq for MB voices
-static const double g_f6522TimerPeriod_NoIRQ = CLK_6502 / 60.0;		// Constant whatever the CLK is set to
+// NB. Not important if NTSC or PAL - just need to pick a sensible period
+static const double g_f6522TimerPeriod_NoIRQ = CLK_6502_NTSC / 60.0;	// Constant whatever the CLK is set to

 static bool g_bCritSectionValid = false;	// Deleting CritialSection when not valid causes crash on Win98
 static CRITICAL_SECTION g_CriticalSection;	// To guard 6522's IFR
@ -1627,7 +1628,7 @@ static BYTE __stdcall PhasorIO(WORD PC, WORD nAddr, BYTE bWrite, BYTE nValue, UL

 	g_PhasorClockScaleFactor = (nAddr & 4) ? 2 : 1;

-	AY8910_InitClock((int)(CLK_6502 * g_PhasorClockScaleFactor));
+	AY8910_InitClock((int)(Get6502BaseClock() * g_PhasorClockScaleFactor));

 	return MemReadFloatingBus(nExecutedCycles);
 }
@ -2189,7 +2190,7 @@ bool MB_LoadSnapshot(YamlLoadHelper& yamlLoadHelper, UINT slot, UINT version)
 		pMB++;
 	}

-	AY8910_InitClock((int)CLK_6502);
+	AY8910_InitClock((int)Get6502BaseClock());

 	// NB. g_SoundcardType & g_bPhasorEnable setup in MB_InitializeIO() -> MB_SetSoundcardType()

@ -2312,7 +2313,7 @@ bool Phasor_LoadSnapshot(YamlLoadHelper& yamlLoadHelper, UINT slot, UINT version
 		pMB++;
 	}

-	AY8910_InitClock((int)(CLK_6502 * g_PhasorClockScaleFactor));
+	AY8910_InitClock((int)(Get6502BaseClock() * g_PhasorClockScaleFactor));

 	// NB. g_SoundcardType & g_bPhasorEnable setup in MB_InitializeIO() -> MB_SetSoundcardType()

--- a/source/NTSC.cpp
+++ b/source/NTSC.cpp
@ -134,7 +134,13 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 	// "There are exactly 17030 (65 x 262) 6502 cycles in every television scan of an American Apple."
 	#define VIDEO_SCANNER_MAX_HORZ   65 // TODO: use Video.cpp: kHClocks
 	#define VIDEO_SCANNER_MAX_VERT  262 // TODO: use Video.cpp: kNTSCScanLines
-	static const int VIDEO_SCANNER_6502_CYCLES = VIDEO_SCANNER_MAX_HORZ * VIDEO_SCANNER_MAX_VERT;
+	static const UINT VIDEO_SCANNER_6502_CYCLES = VIDEO_SCANNER_MAX_HORZ * VIDEO_SCANNER_MAX_VERT;
+
+	#define VIDEO_SCANNER_MAX_VERT_PAL 312
+	static const UINT VIDEO_SCANNER_6502_CYCLES_PAL = VIDEO_SCANNER_MAX_HORZ * VIDEO_SCANNER_MAX_VERT_PAL;
+
+	static UINT g_videoScannerMaxVert = VIDEO_SCANNER_MAX_VERT;			// default to NTSC
+	static UINT g_videoScanner6502Cycles = VIDEO_SCANNER_6502_CYCLES;	// default to NTSC

 	#define VIDEO_SCANNER_HORZ_COLORBURST_BEG 12
 	#define VIDEO_SCANNER_HORZ_COLORBURST_END 16
@ -212,9 +218,9 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 // Tables
 	// Video scanner tables are now runtime-generated using UTAIIe logic
-	static unsigned short g_aClockVertOffsetsHGR[VIDEO_SCANNER_MAX_VERT];
-	static unsigned short g_aClockVertOffsetsTXT[33];
-	static unsigned short APPLE_IIP_HORZ_CLOCK_OFFSET[5][VIDEO_SCANNER_MAX_HORZ];
+	static unsigned short g_aClockVertOffsetsHGR[VIDEO_SCANNER_MAX_VERT_PAL];
+	static unsigned short g_aClockVertOffsetsTXT[VIDEO_SCANNER_MAX_VERT_PAL/8];
+	static unsigned short APPLE_IIP_HORZ_CLOCK_OFFSET[5][VIDEO_SCANNER_MAX_HORZ];	// 5 = CEILING(312/64) = CEILING(262/64)
 	static unsigned short APPLE_IIE_HORZ_CLOCK_OFFSET[5][VIDEO_SCANNER_MAX_HORZ];

 #ifdef _DEBUG
@ -243,7 +249,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 		0x0B80,0x0F80,0x1380,0x1780,0x1B80,0x1F80
 	};

-	static unsigned short g_kClockVertOffsetsTXT[33] =
+	static unsigned short g_kClockVertOffsetsTXT[33] =	// 33 = CEILING(262/8)
 	{
 		0x0000,0x0080,0x0100,0x0180,0x0200,0x0280,0x0300,0x0380,
 		0x0000,0x0080,0x0100,0x0180,0x0200,0x0280,0x0300,0x0380,
@ -768,7 +774,7 @@ inline void updateVideoScannerHorzEOLSimple()
 	{
 		g_nVideoClockHorz = 0;

-		if (++g_nVideoClockVert == VIDEO_SCANNER_MAX_VERT)
+		if (++g_nVideoClockVert == g_videoScannerMaxVert)
 		{
 			g_nVideoClockVert = 0;

@ -807,7 +813,7 @@ inline void updateVideoScannerHorzEOL()

 		g_nVideoClockHorz = 0;

-		if (++g_nVideoClockVert == VIDEO_SCANNER_MAX_VERT)
+		if (++g_nVideoClockVert == g_videoScannerMaxVert)
 		{
 			g_nVideoClockVert = 0;

@ -851,7 +857,7 @@ inline void updateVideoScannerHorzEOL_14M()

 		g_nVideoClockHorz = 0;

-		if (++g_nVideoClockVert == VIDEO_SCANNER_MAX_VERT)
+		if (++g_nVideoClockVert == g_videoScannerMaxVert)
 		{
 			g_nVideoClockVert = 0;

@ -897,7 +903,7 @@ inline void updateVideoScannerHorzEOL()

 		g_nVideoClockHorz = 0;

-		if (++g_nVideoClockVert == VIDEO_SCANNER_MAX_VERT)
+		if (++g_nVideoClockVert == g_videoScannerMaxVert)
 		{
 			g_nVideoClockVert = 0;

@ -1838,8 +1844,8 @@ uint32_t*NTSC_VideoGetChromaTable( bool bHueTypeMonochrome, bool bMonitorTypeCol
 //===========================================================================
 void NTSC_VideoClockResync(const DWORD dwCyclesThisFrame)
 {
-	g_nVideoClockVert = (uint16_t) (dwCyclesThisFrame / VIDEO_SCANNER_MAX_HORZ) % VIDEO_SCANNER_MAX_VERT;
-	g_nVideoClockHorz = (uint16_t) (dwCyclesThisFrame % VIDEO_SCANNER_MAX_HORZ);
+	g_nVideoClockVert = (uint16_t)(dwCyclesThisFrame / VIDEO_SCANNER_MAX_HORZ) % g_videoScannerMaxVert;
+	g_nVideoClockHorz = (uint16_t)(dwCyclesThisFrame % VIDEO_SCANNER_MAX_HORZ);
 }

 //===========================================================================
@ -1861,7 +1867,7 @@ uint16_t NTSC_VideoGetScannerAddress ( const ULONG uExecutedCycles )
 		g_nVideoClockHorz += VIDEO_SCANNER_MAX_HORZ;
 		g_nVideoClockVert -= 1;
 		if ((SHORT)g_nVideoClockVert < 0)
-			g_nVideoClockVert = VIDEO_SCANNER_MAX_VERT-1;
+			g_nVideoClockVert = g_videoScannerMaxVert-1;
 	}

 	uint16_t addr;
@ -2154,8 +2160,8 @@ void NTSC_VideoInit( uint8_t* pFramebuffer ) // wsVideoInit
 //===========================================================================
 void NTSC_VideoReinitialize( DWORD cyclesThisFrame, bool bInitVideoScannerAddress )
 {
-	_ASSERT(cyclesThisFrame < VIDEO_SCANNER_6502_CYCLES);
-	if (cyclesThisFrame >= VIDEO_SCANNER_6502_CYCLES) cyclesThisFrame = 0;	// error
+	_ASSERT(cyclesThisFrame < g_videoScanner6502Cycles);
+	if (cyclesThisFrame >= g_videoScanner6502Cycles) cyclesThisFrame = 0;	// error
 	g_nVideoClockVert = (uint16_t) (cyclesThisFrame / VIDEO_SCANNER_MAX_HORZ);
 	g_nVideoClockHorz = cyclesThisFrame % VIDEO_SCANNER_MAX_HORZ;

@ -2193,7 +2199,7 @@ void NTSC_VideoInitChroma()

 //===========================================================================

-// Pre: cyclesLeftToUpdate = [0...VIDEO_SCANNER_6502_CYCLES]
+// Pre: cyclesLeftToUpdate = [0...g_videoScanner6502Cycles]
 // .  2-14: After one emulated 6502/65C02 opcode (optionally with IRQ)
 // . ~1000: After 1ms of Z80 emulation
 // . 17030: From NTSC_VideoRedrawWholeScreen()
@ -2208,7 +2214,7 @@ static void VideoUpdateCycles( int cyclesLeftToUpdate )
 		g_pFuncUpdateGraphicsScreen(cycles);						// lines [currV...159]
 		cyclesLeftToUpdate -= cycles;

-		const int cyclesFromLine160ToLine261 = VIDEO_SCANNER_6502_CYCLES - (VIDEO_SCANNER_MAX_HORZ * VIDEO_SCANNER_Y_MIXED);
+		const int cyclesFromLine160ToLine261 = g_videoScanner6502Cycles - (VIDEO_SCANNER_MAX_HORZ * VIDEO_SCANNER_Y_MIXED);
 		cycles = cyclesLeftToUpdate < cyclesFromLine160ToLine261 ? cyclesLeftToUpdate : cyclesFromLine160ToLine261;
 		g_pFuncUpdateGraphicsScreen(cycles);						// lines [160..191..261]
 		cyclesLeftToUpdate -= cycles;
@ -2217,7 +2223,7 @@ static void VideoUpdateCycles( int cyclesLeftToUpdate )
 	}
 	else
 	{
-		const int cyclesToLine262 = VIDEO_SCANNER_MAX_HORZ * (VIDEO_SCANNER_MAX_VERT - g_nVideoClockVert - 1) + cyclesToEndOfLine;
+		const int cyclesToLine262 = VIDEO_SCANNER_MAX_HORZ * (g_videoScannerMaxVert - g_nVideoClockVert - 1) + cyclesToEndOfLine;
 		int cycles = cyclesLeftToUpdate < cyclesToLine262 ? cyclesLeftToUpdate : cyclesToLine262;
 		g_pFuncUpdateGraphicsScreen(cycles);						// lines [currV...261]
 		cyclesLeftToUpdate -= cycles;
@ -2235,9 +2241,9 @@ static void VideoUpdateCycles( int cyclesLeftToUpdate )
 }

 //===========================================================================
-void NTSC_VideoUpdateCycles( long cycles6502 )
+void NTSC_VideoUpdateCycles( UINT cycles6502 )
 {
-	_ASSERT(cycles6502 && cycles6502 < VIDEO_SCANNER_6502_CYCLES);	// Use NTSC_VideoRedrawWholeScreen() instead
+	_ASSERT(cycles6502 && cycles6502 < g_videoScanner6502Cycles);	// Use NTSC_VideoRedrawWholeScreen() instead

 	if (g_bDelayVideoMode)
 	{
@ -2269,7 +2275,7 @@ void NTSC_VideoRedrawWholeScreen( void )
 	g_nVideoClockHorz = 0;
 	updateVideoScannerAddress();

-	VideoUpdateCycles(VIDEO_SCANNER_6502_CYCLES);
+	VideoUpdateCycles(g_videoScanner6502Cycles);

 	VideoUpdateCycles(horz);	// Finally update to get to correct H-pos

@ -2324,19 +2330,37 @@ static void CheckVideoTables( void )
 	CheckVideoTables2(A2TYPE_APPLE2E,    VF_TEXT);
 }

+static bool IsNTSC(void)
+{
+	return g_videoScannerMaxVert == VIDEO_SCANNER_MAX_VERT;
+}
+
 static void GenerateVideoTables( void )
 {
 	eApple2Type currentApple2Type = GetApple2Type();
+	uint32_t currentVideoMode = g_uVideoMode;
+	int currentHiresPage = g_nHiresPage;
+	int currentTextPage = g_nTextPage;
+
+	g_nHiresPage = g_nTextPage = 1;

 	//
 	// g_aClockVertOffsetsHGR[]
 	//

 	g_uVideoMode = VF_HIRES;
-	for (UINT i=0, cycle=VIDEO_SCANNER_HORZ_START; i<VIDEO_SCANNER_MAX_VERT; i++, cycle+=VIDEO_SCANNER_MAX_HORZ)
 	{
-		g_aClockVertOffsetsHGR[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
-		_ASSERT(g_aClockVertOffsetsHGR[i] == g_kClockVertOffsetsHGR[i]);
+		UINT i = 0, cycle = VIDEO_SCANNER_HORZ_START;
+		for (; i < VIDEO_SCANNER_MAX_VERT; i++, cycle += VIDEO_SCANNER_MAX_HORZ)
+		{
+			g_aClockVertOffsetsHGR[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
+			if (IsNTSC()) _ASSERT(g_aClockVertOffsetsHGR[i] == g_kClockVertOffsetsHGR[i]);
+		}
+		if (!IsNTSC())
+		{
+			for (; i < VIDEO_SCANNER_MAX_VERT_PAL; i++, cycle += VIDEO_SCANNER_MAX_HORZ)
+				g_aClockVertOffsetsHGR[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
+		}
 	}

 	//
@ -2344,10 +2368,18 @@ static void GenerateVideoTables( void )
 	//

 	g_uVideoMode = VF_TEXT;
-	for (UINT i=0, cycle=VIDEO_SCANNER_HORZ_START; i<(256+8)/8; i++, cycle+=VIDEO_SCANNER_MAX_HORZ*8)
 	{
-		g_aClockVertOffsetsTXT[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
-		_ASSERT(g_aClockVertOffsetsTXT[i] == g_kClockVertOffsetsTXT[i]);
+		UINT i = 0, cycle = VIDEO_SCANNER_HORZ_START;
+		for (; i < (256 + 8) / 8; i++, cycle += VIDEO_SCANNER_MAX_HORZ * 8)
+		{
+			g_aClockVertOffsetsTXT[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
+			if (IsNTSC()) _ASSERT(g_aClockVertOffsetsTXT[i] == g_kClockVertOffsetsTXT[i]);
+		}
+		if (!IsNTSC())
+		{
+			for (; i < VIDEO_SCANNER_MAX_VERT_PAL / 8; i++, cycle += VIDEO_SCANNER_MAX_HORZ * 8)
+				g_aClockVertOffsetsTXT[i] = VideoGetScannerAddress(cycle, VS_PartialAddrV);
+		}
 	}

 	//
@ -2361,7 +2393,7 @@ static void GenerateVideoTables( void )
 		for (UINT i=0, cycle=j*64*VIDEO_SCANNER_MAX_HORZ; i<VIDEO_SCANNER_MAX_HORZ; i++, cycle++)
 		{
 			APPLE_IIP_HORZ_CLOCK_OFFSET[j][i] = VideoGetScannerAddress(cycle, VS_PartialAddrH);
-			_ASSERT(APPLE_IIP_HORZ_CLOCK_OFFSET[j][i] == kAPPLE_IIP_HORZ_CLOCK_OFFSET[j][i]);
+			if (IsNTSC()) _ASSERT(APPLE_IIP_HORZ_CLOCK_OFFSET[j][i] == kAPPLE_IIP_HORZ_CLOCK_OFFSET[j][i]);
 		}
 	}

@ -2376,7 +2408,7 @@ static void GenerateVideoTables( void )
 		for (UINT i=0, cycle=j*64*VIDEO_SCANNER_MAX_HORZ; i<VIDEO_SCANNER_MAX_HORZ; i++, cycle++)
 		{
 			APPLE_IIE_HORZ_CLOCK_OFFSET[j][i] = VideoGetScannerAddress(cycle, VS_PartialAddrH);
-			_ASSERT(APPLE_IIE_HORZ_CLOCK_OFFSET[j][i] == kAPPLE_IIE_HORZ_CLOCK_OFFSET[j][i]);
+			if (IsNTSC()) _ASSERT(APPLE_IIE_HORZ_CLOCK_OFFSET[j][i] == kAPPLE_IIE_HORZ_CLOCK_OFFSET[j][i]);
 		}
 	}

@ -2384,11 +2416,15 @@ static void GenerateVideoTables( void )

 	CheckVideoTables();

-	VideoResetState();
+//	VideoResetState();
+
 	SetApple2Type(currentApple2Type);
+	g_uVideoMode = currentVideoMode;
+	g_nHiresPage = currentHiresPage;
+	g_nTextPage = currentTextPage;
 }

-void GenerateBaseColors(baseColors_t pBaseNtscColors)
+static void GenerateBaseColors(baseColors_t pBaseNtscColors)
 {
 	for (UINT i=0; i<16; i++)
 	{
@ -2415,3 +2451,26 @@ void GenerateBaseColors(baseColors_t pBaseNtscColors)
 		(*pBaseNtscColors)[i] = * (bgra_t*) &color;
 	}
 }
+
+//===========================================================================
+
+void NTSC_SetRefreshRate(VideoRefreshRate_e rate)
+{
+	if (rate == VR_50HZ)
+	{
+		g_videoScannerMaxVert = VIDEO_SCANNER_MAX_VERT_PAL;
+		g_videoScanner6502Cycles = VIDEO_SCANNER_6502_CYCLES_PAL;
+	}
+	else
+	{
+		g_videoScannerMaxVert = VIDEO_SCANNER_MAX_VERT;
+		g_videoScanner6502Cycles = VIDEO_SCANNER_6502_CYCLES;
+	}
+
+	GenerateVideoTables();
+}
+
+UINT NTSC_GetCyclesPerFrame(void)
+{
+	return g_videoScanner6502Cycles;
+}
--- a/source/NTSC.h
+++ b/source/NTSC.h
@ -14,6 +14,10 @@
 	extern void     NTSC_VideoReinitialize( DWORD cyclesThisFrame, bool bInitVideoScannerAddress );
 	extern void     NTSC_VideoInitAppleType();
 	extern void     NTSC_VideoInitChroma();
-	extern void     NTSC_VideoUpdateCycles( long cycles6502 );
+	extern void     NTSC_VideoUpdateCycles( UINT cycles6502 );
 	extern void     NTSC_VideoRedrawWholeScreen( void );
 	extern UINT     NTSC_GetFrameBufferBorderlessWidth( void );
+
+	enum VideoRefreshRate_e;
+	void NTSC_SetRefreshRate(VideoRefreshRate_e rate);
+	UINT NTSC_GetCyclesPerFrame(void);
--- a/source/SaveState.cpp
+++ b/source/SaveState.cpp
@ -67,7 +67,8 @@ static YamlHelper yamlHelper;
 // Unit version history:
 // v2: Extended: keyboard (added 'Key Waiting'), memory (LC mem type for II/II+, inverted MF_INTCXROM bit)
 // v3: Extended: memory (added 'AnnunciatorN')
-#define UNIT_APPLE2_VER 3
+// v4: Extended: video (added 'Video Refresh Rate')
+#define UNIT_APPLE2_VER 4

 #define UNIT_SLOTS_VER 1

@ -219,7 +220,7 @@ static void ParseUnitApple2(YamlLoadHelper& yamlLoadHelper, UINT version)
 	JoyLoadSnapshot(yamlLoadHelper);
 	KeybLoadSnapshot(yamlLoadHelper, version);
 	SpkrLoadSnapshot(yamlLoadHelper);
-	VideoLoadSnapshot(yamlLoadHelper);
+	VideoLoadSnapshot(yamlLoadHelper, version);
 	MemLoadSnapshot(yamlLoadHelper, version);

 	// g_Apple2Type may've changed: so redraw frame (title, buttons, leds, etc)
@ -395,6 +396,7 @@ static void Snapshot_LoadState_v2(void)
 		HD_Reset();
 		KeybReset();
 		VideoResetState();
+		SetVideoRefreshRate(VR_60HZ);		// Default to 60Hz as older save-states won't contain refresh rate
 		MB_InitializeForLoadingSnapshot();	// GH#609
 		sg_SSC.CommReset();
 #ifdef USE_SPEECH_API
@ -420,7 +422,7 @@ static void Snapshot_LoadState_v2(void)
 		// . A change in h/w via loading a save-state avoids this VM restart
 		// The latter is the desired approach (as the former needs a "power-on" / F2 to start things again)

-		sg_PropertySheet.ApplyNewConfig(m_ConfigNew, ConfigOld);
+		sg_PropertySheet.ApplyNewConfig(m_ConfigNew, ConfigOld);	// Mainly just saves (some) new state to Registry

 		MemInitializeROM();
 		MemInitializeCustomF8ROM();
--- a/source/Video.cpp
+++ b/source/Video.cpp
@ -91,7 +91,7 @@ uint32_t  g_uVideoMode     = VF_TEXT; // Current Video Mode (this is the last se
 DWORD     g_eVideoType     = VT_DEFAULT;
 static VideoStyle_e g_eVideoStyle = VS_HALF_SCANLINES;

-static const bool g_bVideoScannerNTSC = true;  // NTSC video scanning (or PAL)
+static bool g_bVideoScannerNTSC = true;  // NTSC video scanning (or PAL)

 //-------------------------------------

@ -542,6 +542,9 @@ void VideoRedrawScreenDuringFullSpeed(DWORD dwCyclesThisFrame, bool bInit /*=fal

 void VideoRedrawScreenAfterFullSpeed(DWORD dwCyclesThisFrame)
 {
+#if 1
+	NTSC_VideoClockResync(dwCyclesThisFrame);
+#else
 	if (g_bVideoScannerNTSC)
 	{
 		NTSC_VideoClockResync(dwCyclesThisFrame);
@ -552,6 +555,7 @@ void VideoRedrawScreenAfterFullSpeed(DWORD dwCyclesThisFrame)
 		g_nVideoClockVert = (uint16_t) (dwCyclesThisFrame / kHClocks) % kPALScanLines;
 		g_nVideoClockHorz = (uint16_t) (dwCyclesThisFrame % kHClocks);
 	}
+#endif

 	VideoRedrawScreen();	// Better (no flicker) than using: NTSC_VideoReinitialize() or VideoReinitialize()
 }
@ -730,9 +734,10 @@ bool VideoGetSWAltCharSet(void)

 //===========================================================================

-#define SS_YAML_KEY_ALTCHARSET "Alt Char Set"
-#define SS_YAML_KEY_VIDEOMODE "Video Mode"
-#define SS_YAML_KEY_CYCLESTHISFRAME "Cycles This Frame"
+#define SS_YAML_KEY_ALT_CHARSET "Alt Char Set"
+#define SS_YAML_KEY_VIDEO_MODE "Video Mode"
+#define SS_YAML_KEY_CYCLES_THIS_FRAME "Cycles This Frame"
+#define SS_YAML_KEY_VIDEO_REFRESH_RATE "Video Refresh Rate"

 static std::string VideoGetSnapshotStructName(void)
 {
@ -743,19 +748,27 @@ static std::string VideoGetSnapshotStructName(void)
 void VideoSaveSnapshot(YamlSaveHelper& yamlSaveHelper)
 {
 	YamlSaveHelper::Label state(yamlSaveHelper, "%s:\n", VideoGetSnapshotStructName().c_str());
-	yamlSaveHelper.SaveBool(SS_YAML_KEY_ALTCHARSET, g_nAltCharSetOffset ? true : false);
-	yamlSaveHelper.SaveHexUint32(SS_YAML_KEY_VIDEOMODE, g_uVideoMode);
-	yamlSaveHelper.SaveUint(SS_YAML_KEY_CYCLESTHISFRAME, g_dwCyclesThisFrame);
+	yamlSaveHelper.SaveBool(SS_YAML_KEY_ALT_CHARSET, g_nAltCharSetOffset ? true : false);
+	yamlSaveHelper.SaveHexUint32(SS_YAML_KEY_VIDEO_MODE, g_uVideoMode);
+	yamlSaveHelper.SaveUint(SS_YAML_KEY_CYCLES_THIS_FRAME, g_dwCyclesThisFrame);
+	yamlSaveHelper.SaveUint(SS_YAML_KEY_VIDEO_REFRESH_RATE, (UINT)GetVideoRefreshRate());
 }

-void VideoLoadSnapshot(YamlLoadHelper& yamlLoadHelper)
+void VideoLoadSnapshot(YamlLoadHelper& yamlLoadHelper, UINT version)
 {
 	if (!yamlLoadHelper.GetSubMap(VideoGetSnapshotStructName()))
 		return;

-	g_nAltCharSetOffset = yamlLoadHelper.LoadBool(SS_YAML_KEY_ALTCHARSET) ? 256 : 0;
-	g_uVideoMode = yamlLoadHelper.LoadUint(SS_YAML_KEY_VIDEOMODE);
-	g_dwCyclesThisFrame = yamlLoadHelper.LoadUint(SS_YAML_KEY_CYCLESTHISFRAME);
+	if (version >= 4)
+	{
+		VideoRefreshRate_e rate = (VideoRefreshRate_e)yamlLoadHelper.LoadUint(SS_YAML_KEY_VIDEO_REFRESH_RATE);
+		SetVideoRefreshRate(rate);	// Trashes: g_dwCyclesThisFrame
+		SetCurrentCLK6502();
+	}
+
+	g_nAltCharSetOffset = yamlLoadHelper.LoadBool(SS_YAML_KEY_ALT_CHARSET) ? 256 : 0;
+	g_uVideoMode = yamlLoadHelper.LoadUint(SS_YAML_KEY_VIDEO_MODE);
+	g_dwCyclesThisFrame = yamlLoadHelper.LoadUint(SS_YAML_KEY_CYCLES_THIS_FRAME);

 	yamlLoadHelper.PopMap();
 }
@ -777,7 +790,7 @@ WORD VideoGetScannerAddress(DWORD nCycles, VideoScanner_e videoScannerAddr /*= V
    //
    const int kScanLines  = g_bVideoScannerNTSC ? kNTSCScanLines : kPALScanLines;
    const int kScanCycles = kScanLines * kHClocks;
-    _ASSERT(nCycles < kScanCycles);
+    _ASSERT(nCycles < (UINT)kScanCycles);
    nCycles %= kScanCycles;

    // calculate horizontal scanning state
@ -795,7 +808,7 @@ WORD VideoGetScannerAddress(DWORD nCycles, VideoScanner_e videoScannerAddr /*= V
    int h_4 = (nHState >> 4) & 1;
    int h_5 = (nHState >> 5) & 1;

-    // calculate vertical scanning state
+    // calculate vertical scanning state (UTAIIe:3-15,T3.2)
    //
    int nVLine  = nCycles / kHClocks; // which vertical scanning line
    int nVState = kVLine0State + nVLine; // V state bits
@ -868,7 +881,7 @@ WORD VideoGetScannerAddress(DWORD nCycles, VideoScanner_e videoScannerAddr /*= V
        nAddressP |= p2b << 11; // a11
 	}

-	// VBL' = v_4' | v_3' = (v_4 & v_3)' (UTAIIe:5-10,#3)
+	// VBL' = v_4' | v_3' = (v_4 & v_3)' (UTAIIe:5-10,#3),  (UTAIIe:3-15,T3.2)

 	if (videoScannerAddr == VS_PartialAddrH)
 		return nAddressH;
@ -1231,6 +1244,10 @@ void Config_Load_Video()
 	REGLOAD(TEXT(REGVALUE_VIDEO_STYLE)     ,(DWORD*)&g_eVideoStyle);
 	REGLOAD(TEXT(REGVALUE_VIDEO_MONO_COLOR),&g_nMonochromeRGB);

+	DWORD rate = VR_60HZ;
+	REGLOAD(TEXT(REGVALUE_VIDEO_REFRESH_RATE), &rate);
+	SetVideoRefreshRate((VideoRefreshRate_e)rate);
+
 	//

 	const UINT16* pOldVersion = GetOldAppleWinVersion();
@ -1275,6 +1292,7 @@ void Config_Save_Video()
 	REGSAVE(TEXT(REGVALUE_VIDEO_MODE)      ,g_eVideoType);
 	REGSAVE(TEXT(REGVALUE_VIDEO_STYLE)     ,g_eVideoStyle);
 	REGSAVE(TEXT(REGVALUE_VIDEO_MONO_COLOR),g_nMonochromeRGB);
+	REGSAVE(TEXT(REGVALUE_VIDEO_REFRESH_RATE), GetVideoRefreshRate());
 }

 //===========================================================================
@ -1305,6 +1323,22 @@ bool IsVideoStyle(VideoStyle_e mask)
 	return (g_eVideoStyle & mask) != 0;
 }

+//===========================================================================
+
+VideoRefreshRate_e GetVideoRefreshRate(void)
+{
+	return (g_bVideoScannerNTSC == false) ? VR_50HZ : VR_60HZ;
+}
+
+void SetVideoRefreshRate(VideoRefreshRate_e rate)
+{
+	if (rate != VR_50HZ)
+		rate = VR_60HZ;
+
+	g_bVideoScannerNTSC = (rate == VR_60HZ);
+	NTSC_SetRefreshRate(rate);
+}
+
 //===========================================================================
 static void videoCreateDIBSection()
 {
--- a/source/Video.h
+++ b/source/Video.h
@ -29,6 +29,13 @@
 //		VS_TEXT_OPTIMIZED=4,
 	};

+	enum VideoRefreshRate_e
+	{
+		VR_NONE,
+		VR_50HZ,
+		VR_60HZ
+	};
+
 	enum VideoFlag_e
 	{
 		VF_80COL  = 0x00000001,
@ -193,7 +200,7 @@ bool    VideoGetSWTEXT(void);
 bool    VideoGetSWAltCharSet(void);

 void    VideoSaveSnapshot(class YamlSaveHelper& yamlSaveHelper);
-void    VideoLoadSnapshot(class YamlLoadHelper& yamlLoadHelper);
+void    VideoLoadSnapshot(class YamlLoadHelper& yamlLoadHelper, UINT version);

 extern bool g_bDisplayPrintScreenFileName;
 extern bool g_bShowPrintScreenWarningDialog;
@ -226,3 +233,6 @@ void SetVideoType(VideoType_e newVideoType);
 VideoStyle_e GetVideoStyle(void);
 void SetVideoStyle(VideoStyle_e newVideoStyle);
 bool IsVideoStyle(VideoStyle_e mask);
+
+VideoRefreshRate_e GetVideoRefreshRate(void);
+void SetVideoRefreshRate(VideoRefreshRate_e rate);
--- a/source/Z80VICE/z80.cpp
+++ b/source/Z80VICE/z80.cpp
@ -5510,7 +5510,10 @@ static void opcode_fd(BYTE ip1, BYTE ip2, BYTE ip3, WORD ip12, WORD ip23)

 /* Z80 mainloop.  */

-static const double uZ80ClockMultiplier = CLK_Z80 / CLK_6502;
+// The effective Z-80 clock rate is 2.041MHz
+// See: http://www.apple2info.net/hardware/softcard/SC-SWHW_a2in.pdf
+static const double uZ80ClockMultiplier = 2;
+
 inline static ULONG ConvertZ80TStatesTo6502Cycles(UINT uTStates)
 {
 	return (uTStates < 0) ? 0 : (ULONG) ((double)uTStates / uZ80ClockMultiplier);