diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 3e4acf185..30a5574bb 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -403,6 +403,7 @@
 		4BD69F941D98760000243FE1 /* AcornADF.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BD69F921D98760000243FE1 /* AcornADF.cpp */; };
 		4BE77A2E1D84ADFB00BC3827 /* File.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BE77A2C1D84ADFB00BC3827 /* File.cpp */; };
 		4BE7C9181E3D397100A5496D /* TIA.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BE7C9161E3D397100A5496D /* TIA.cpp */; };
+		4BE9A6B11EDE293000CBCB47 /* zexdoc.com in Resources */ = {isa = PBXBuildFile; fileRef = 4BE9A6B01EDE293000CBCB47 /* zexdoc.com */; };
 		4BEA525E1DF33323007E74F2 /* Tape.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BEA525D1DF33323007E74F2 /* Tape.cpp */; };
 		4BEA52631DF339D7007E74F2 /* Speaker.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BEA52611DF339D7007E74F2 /* Speaker.cpp */; };
 		4BEA52661DF3472B007E74F2 /* Speaker.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BEA52641DF3472B007E74F2 /* Speaker.cpp */; };
@@ -944,6 +945,7 @@
 		4BE77A2D1D84ADFB00BC3827 /* File.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; name = File.hpp; path = ../../StaticAnalyser/Commodore/File.hpp; sourceTree = "<group>"; };
 		4BE7C9161E3D397100A5496D /* TIA.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = TIA.cpp; sourceTree = "<group>"; };
 		4BE7C9171E3D397100A5496D /* TIA.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = TIA.hpp; sourceTree = "<group>"; };
+		4BE9A6B01EDE293000CBCB47 /* zexdoc.com */ = {isa = PBXFileReference; lastKnownFileType = file; name = zexdoc.com; path = Zexall/zexdoc.com; sourceTree = "<group>"; };
 		4BEA525D1DF33323007E74F2 /* Tape.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = Tape.cpp; path = Electron/Tape.cpp; sourceTree = "<group>"; };
 		4BEA525F1DF333D8007E74F2 /* Tape.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; name = Tape.hpp; path = Electron/Tape.hpp; sourceTree = "<group>"; };
 		4BEA52601DF3343A007E74F2 /* Interrupts.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; name = Interrupts.hpp; path = Electron/Interrupts.hpp; sourceTree = "<group>"; };
@@ -1050,7 +1052,7 @@
 				4B44EBF81DC9898E00A7820C /* BCDTEST_beeb */,
 				4B44EBF61DC9883B00A7820C /* 6502_functional_test.bin */,
 				4B44EBF41DC987AE00A7820C /* AllSuiteA.bin */,
-				4BFCA1281ECBE7A700AC40C1 /* zexall.com */,
+				4BE9A6B21EDE294200CBCB47 /* Zexall */,
 				4BBF49B41ED2881600AB3669 /* FUSE */,
 				4BB297E41B587D8300A49093 /* Wolfgang Lorenz 6502 test suite */,
 			);
@@ -2003,6 +2005,15 @@
 			path = Resources;
 			sourceTree = "<group>";
 		};
+		4BE9A6B21EDE294200CBCB47 /* Zexall */ = {
+			isa = PBXGroup;
+			children = (
+				4BFCA1281ECBE7A700AC40C1 /* zexall.com */,
+				4BE9A6B01EDE293000CBCB47 /* zexdoc.com */,
+			);
+			name = Zexall;
+			sourceTree = "<group>";
+		};
 		4BEAC0801E7E0DF800EE56B2 /* Cartridges */ = {
 			isa = PBXGroup;
 			children = (
@@ -2370,6 +2381,7 @@
 				4BB299781B587D8400A49093 /* ldaix in Resources */,
 				4B44EBF71DC9883B00A7820C /* 6502_functional_test.bin in Resources */,
 				4BB299291B587D8400A49093 /* cia2pb7 in Resources */,
+				4BE9A6B11EDE293000CBCB47 /* zexdoc.com in Resources */,
 				4BB2994A1B587D8400A49093 /* deca in Resources */,
 				4BB299CA1B587D8400A49093 /* sbciy in Resources */,
 				4BB2993D1B587D8400A49093 /* cpxa in Resources */,
diff --git a/OSBindings/Mac/Clock SignalTests/ZexallTests.swift b/OSBindings/Mac/Clock SignalTests/ZexallTests.swift
index 8931cfdd8..ddc0ba893 100644
--- a/OSBindings/Mac/Clock SignalTests/ZexallTests.swift	
+++ b/OSBindings/Mac/Clock SignalTests/ZexallTests.swift	
@@ -15,7 +15,7 @@ class ZexallTests: XCTestCase, CSTestMachineTrapHandler {
 	fileprivate var output = ""
 
 	func testZexall() {
-		if let filename = Bundle(for: type(of: self)).path(forResource: "zexall", ofType: "com") {
+		if let filename = Bundle(for: type(of: self)).path(forResource: "zexdoc", ofType: "com") {
 			if let testData = try? Data(contentsOf: URL(fileURLWithPath: filename)) {
 
 				// install test program, at the usual CP/M place
@@ -33,16 +33,100 @@ class ZexallTests: XCTestCase, CSTestMachineTrapHandler {
 				// CP/M programs can exit
 				machine.addTrapAddress(0);
 
+				// ensure that if the CPU hits zero, it stays there until the end of the
+				// sampling window
+				machine.setValue(0xc3, atAddress: 0x0000)
+				machine.setValue(0x00, atAddress: 0x0001)
+				machine.setValue(0x00, atAddress: 0x0002)
+
 				// seed execution at 0x0100
 				machine.setValue(0x0100, for: .programCounter)
 
 				// run!
+				let cyclesPerIteration: Int32 = 400_000_000
+				var cyclesToDate: TimeInterval = 0
+				let startDate = Date()
+				var printDate = Date()
 				while !done {
-					machine.runForNumber(ofCycles: 200)
+					machine.runForNumber(ofCycles: cyclesPerIteration)
+					cyclesToDate += TimeInterval(cyclesPerIteration)
+					if printDate.timeIntervalSinceNow < -5.0 {
+						print("\(cyclesToDate / -startDate.timeIntervalSinceNow) Mhz")
+						printDate = Date()
+					}
 				}
 
-				print("Done!")
-				print(output)
+				let targetOutput =
+					"Z80doc instruction exerciser\n\r"			+
+					"<adc,sbc> hl,<bc,de,hl,sp>....  OK\n\r"	+
+					"add hl,<bc,de,hl,sp>..........  OK\n\r"	+
+					"add ix,<bc,de,ix,sp>..........  OK\n\r"	+
+					"add iy,<bc,de,iy,sp>..........  OK\n\r"	+
+					"aluop a,nn....................  OK\n\r"	+
+					"aluop a,<b,c,d,e,h,l,(hl),a>..  OK\n\r"	+
+					"aluop a,<ixh,ixl,iyh,iyl>.....  OK\n\r"	+
+					"aluop a,(<ix,iy>+1)...........  OK\n\r"	+
+					"bit n,(<ix,iy>+1).............  OK\n\r"	+
+					"bit n,<b,c,d,e,h,l,(hl),a>....  OK\n\r"	+
+					"cpd<r>........................  OK\n\r"	+
+					"cpi<r>........................  OK\n\r"	+
+					"<daa,cpl,scf,ccf>.............  OK\n\r"	+
+					"<inc,dec> a...................  OK\n\r"	+
+					"<inc,dec> b...................  OK\n\r"	+
+					"<inc,dec> bc..................  OK\n\r"	+
+					"<inc,dec> c...................  OK\n\r"	+
+					"<inc,dec> d...................  OK\n\r"	+
+					"<inc,dec> de..................  OK\n\r"	+
+					"<inc,dec> e...................  OK\n\r"	+
+					"<inc,dec> h...................  OK\n\r"	+
+					"<inc,dec> hl..................  OK\n\r"	+
+					"<inc,dec> ix..................  OK\n\r"	+
+					"<inc,dec> iy..................  OK\n\r"	+
+					"<inc,dec> l...................  OK\n\r"	+
+					"<inc,dec> (hl)................  OK\n\r"	+
+					"<inc,dec> sp..................  OK\n\r"	+
+					"<inc,dec> (<ix,iy>+1).........  OK\n\r"	+
+					"<inc,dec> ixh.................  OK\n\r"	+
+					"<inc,dec> ixl.................  OK\n\r"	+
+					"<inc,dec> iyh.................  OK\n\r"	+
+					"<inc,dec> iyl.................  OK\n\r"	+
+					"ld <bc,de>,(nnnn).............  OK\n\r"	+
+					"ld hl,(nnnn)..................  OK\n\r"	+
+					"ld sp,(nnnn)..................  OK\n\r"	+
+					"ld <ix,iy>,(nnnn).............  OK\n\r"	+
+					"ld (nnnn),<bc,de>.............  OK\n\r"	+
+					"ld (nnnn),hl..................  OK\n\r"	+
+					"ld (nnnn),sp..................  OK\n\r"	+
+					"ld (nnnn),<ix,iy>.............  OK\n\r"	+
+					"ld <bc,de,hl,sp>,nnnn.........  OK\n\r"	+
+					"ld <ix,iy>,nnnn...............  OK\n\r"	+
+					"ld a,<(bc),(de)>..............  OK\n\r"	+
+					"ld <b,c,d,e,h,l,(hl),a>,nn....  OK\n\r"	+
+					"ld (<ix,iy>+1),nn.............  OK\n\r"	+
+					"ld <b,c,d,e>,(<ix,iy>+1)......  OK\n\r"	+
+					"ld <h,l>,(<ix,iy>+1)..........  OK\n\r"	+
+					"ld a,(<ix,iy>+1)..............  OK\n\r"	+
+					"ld <ixh,ixl,iyh,iyl>,nn.......  OK\n\r"	+
+					"ld <bcdehla>,<bcdehla>........  OK\n\r"	+
+					"ld <bcdexya>,<bcdexya>........  OK\n\r"	+
+					"ld a,(nnnn) / ld (nnnn),a.....  OK\n\r"	+
+					"ldd<r> (1)....................  OK\n\r"	+
+					"ldd<r> (2)....................  OK\n\r"	+
+					"ldi<r> (1)....................  OK\n\r"	+
+					"ldi<r> (2)....................  OK\n\r"	+
+					"neg...........................  OK\n\r"	+
+					"<rrd,rld>.....................  OK\n\r"	+
+					"<rlca,rrca,rla,rra>...........  OK\n\r"	+
+					"shf/rot (<ix,iy>+1)...........  OK\n\r"	+
+					"shf/rot <b,c,d,e,h,l,(hl),a>..  OK\n\r"	+
+					"<set,res> n,<bcdehl(hl)a>.....  OK\n\r"	+
+					"<set,res> n,(<ix,iy>+1).......  OK\n\r"	+
+					"ld (<ix,iy>+1),<b,c,d,e>......  OK\n\r"	+
+					"ld (<ix,iy>+1),<h,l>..........  OK\n\r"	+
+					"ld (<ix,iy>+1),a..............  OK\n\r"	+
+					"ld (<bc,de>),a................  OK\n\r"	+
+					"Tests complete\n\r"
+				XCTAssertEqual(targetOutput, output);
 			}
 		}
 	}
@@ -51,6 +135,7 @@ class ZexallTests: XCTestCase, CSTestMachineTrapHandler {
 		switch address {
 			case 0x0005:
 				let cRegister = testMachine.value(for: .C)
+				var textToAppend = ""
 				switch cRegister {
 					case 9:
 						var address = testMachine.value(for: .DE)
@@ -60,17 +145,18 @@ class ZexallTests: XCTestCase, CSTestMachineTrapHandler {
 							if character == "$" {
 								break
 							}
-							output = output + String(character)
+							textToAppend += String(character)
 							address = address + 1
 						}
 					case 5:
-						output += String(describing: UnicodeScalar(testMachine.value(for: .E)))
+						textToAppend = String(describing: UnicodeScalar(testMachine.value(for: .E)))
 					case 0:
 						done = true
 					default:
 						break
 				}
-				print(output)
+				print(textToAppend)
+
 			case 0x0000:
 				done = true