diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 65a4ea339..7ffa65dc6 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -560,7 +560,7 @@ void Base<personality>::write_register(uint8_t value) {
 	write_phase_ = false;
 	if(value & 0x80) {
 		if constexpr (is_yamaha_vdp(personality)) {
-			value &= 0x7f;
+			value &= 0x3f;
 		} else if constexpr (is_sega_vdp(personality)) {
 			if(value & 0x40) {
 				Storage<personality>::cram_is_selected_ = true;
@@ -571,17 +571,10 @@ void Base<personality>::write_register(uint8_t value) {
 			value &= 0x7;
 		}
 
-		// This is a write to a register.
+		// This is a write to a register; handle all generic
+		// TMS registers here (with potential extra bits).
 		switch(value) {
 			case 0:
-				if constexpr (is_sega_vdp(personality)) {
-					Storage<personality>::vertical_scroll_lock_ = low_write_ & 0x80;
-					Storage<personality>::horizontal_scroll_lock_ = low_write_ & 0x40;
-					Storage<personality>::hide_left_column_ = low_write_ & 0x20;
-					enable_line_interrupts_ = low_write_ & 0x10;
-					Storage<personality>::shift_sprites_8px_left_ = low_write_ & 0x08;
-					Storage<personality>::mode4_enable_ = low_write_ & 0x04;
-				}
 				mode2_enable_ = low_write_ & 0x02;
 			break;
 
@@ -600,10 +593,6 @@ void Base<personality>::write_register(uint8_t value) {
 
 			case 2:
 				pattern_name_address_ = size_t((low_write_ & 0xf) << 10) | 0x3ff;
-
-				if constexpr (is_sega_vdp(personality)) {
-					Storage<personality>::pattern_name_address_ = pattern_name_address_ | ((personality == TMS::SMSVDP) ? 0x000 : 0x400);
-				}
 			break;
 
 			case 3:
@@ -616,16 +605,10 @@ void Base<personality>::write_register(uint8_t value) {
 
 			case 5:
 				sprite_attribute_table_address_ = size_t((low_write_ & 0x7f) << 7) | 0x7f;
-				if constexpr (is_sega_vdp(personality)) {
-					Storage<personality>::sprite_attribute_table_address_ = sprite_attribute_table_address_ | ((personality == TMS::SMSVDP) ? 0x00 : 0x80);
-				}
 			break;
 
 			case 6:
 				sprite_generator_table_address_ = size_t((low_write_ & 0x07) << 11) | 0x7ff;
-				if constexpr (is_sega_vdp(personality)) {
-					Storage<personality>::sprite_generator_table_address_ = sprite_generator_table_address_ | ((personality == TMS::SMSVDP) ? 0x0000 : 0x1800);
-				}
 			break;
 
 			case 7:
@@ -633,39 +616,196 @@ void Base<personality>::write_register(uint8_t value) {
 				background_colour_ = low_write_ & 0xf;
 			break;
 
-			case 8:
-				if constexpr (is_sega_vdp(personality)) {
+			default: break;
+		}
+
+		if constexpr (is_sega_vdp(personality)) {
+			switch(value) {
+				default: break;
+
+				case 0:
+					Storage<personality>::vertical_scroll_lock_ = low_write_ & 0x80;
+					Storage<personality>::horizontal_scroll_lock_ = low_write_ & 0x40;
+					Storage<personality>::hide_left_column_ = low_write_ & 0x20;
+					enable_line_interrupts_ = low_write_ & 0x10;
+					Storage<personality>::shift_sprites_8px_left_ = low_write_ & 0x08;
+					Storage<personality>::mode4_enable_ = low_write_ & 0x04;
+				break;
+
+				case 2:
+					Storage<personality>::pattern_name_address_ = pattern_name_address_ | ((personality == TMS::SMSVDP) ? 0x000 : 0x400);
+				break;
+
+				case 5:
+					Storage<personality>::sprite_attribute_table_address_ = sprite_attribute_table_address_ | ((personality == TMS::SMSVDP) ? 0x00 : 0x80);
+				break;
+
+				case 6:
+					Storage<personality>::sprite_generator_table_address_ = sprite_generator_table_address_ | ((personality == TMS::SMSVDP) ? 0x0000 : 0x1800);
+				break;
+
+				case 8:
 					Storage<personality>::horizontal_scroll_ = low_write_;
-				} else {
-					LOG("Unknown TMS write: " << int(low_write_) << " to " << int(value));
-				}
-			break;
+				break;
 
-			case 9:
-				if constexpr (is_sega_vdp(personality)) {
+				case 9:
 					Storage<personality>::vertical_scroll_ = low_write_;
-				} else {
-					LOG("Unknown TMS write: " << int(low_write_) << " to " << int(value));
-				}
-			break;
+				break;
 
-			case 10:
-				if constexpr (is_sega_vdp(personality)) {
+				case 10:
 					line_interrupt_target_ = low_write_;
-				} else {
-					LOG("Unknown TMS write: " << int(low_write_) << " to " << int(value));
-				}
-			break;
+				break;
+			}
+		}
 
-			case 15:
-				if constexpr (is_yamaha_vdp(personality)) {
+		if constexpr (is_yamaha_vdp(personality)) {
+			switch(value) {
+				default: break;
+
+				case 0:
+					LOG("TODO: Yamaha additional mode selection; " << PADHEX(2) << +low_write_);
+					// b1–b3: M3–M5
+					// b4: enable horizontal retrace interrupt
+					// b5: enable light pen interrupts
+					// b6: set colour bus to input or output mode
+				break;
+
+				case 8:
+					LOG("TODO: Yamaha VRAM organisation, sprite disable, etc; " << PADHEX(2) << +low_write_);
+					// b7: "1 = input on colour bus, enable mouse; 1 = output on colour bus, disable mouse" [documentation clearly in error]
+					// b6: 1 = enable light pen
+					// b5: sets the colour of code 0 to the colour of the palette (???)
+					// b4: 1 = colour bus in input mode; 0 = colour bus in output mode
+					// b3: 1 = VRAM is 64kx1 or 64kx4; 0 = 16kx1 or 16kx4; affects refresh.
+					// b1: 1 = disable sprites (and release sprite access slots)
+					// b0: 1 = output in grayscale
+				break;
+
+				case 9:
+					LOG("TODO: Yamaha line count, interlace, etc; " << PADHEX(2) << +low_write_);
+					// b7: 1 = 212 lines of pixels; 0 = 192
+					// b5 & b4: select simultaneous mode (seems to relate to line length and in-phase colour?)
+					// b3: 1 = interlace on
+					// b2: 1 = display two graphic screens interchangeably by even/odd field
+					// b1: 1 = PAL mode; 0 = NTSC mode
+					// b0: 1 = [dot clock] DLCLK is input; 0 = DLCLK is output
+				break;
+
+				case 10:
+					LOG("TODO: Yamaha colour table high bits; " << PADHEX(2) << +low_write_);
+					// b0–b2: A14–A16 of the colour table.
+				break;
+
+				case 11:
+					LOG("TODO: Yamaha sprite table high bits; " << PADHEX(2) << +low_write_);
+					// b0–b1: A15–A16 of the sprite table.
+				break;
+
+				case 12:
+					LOG("TODO: Yamaha text and background blink colour; " << PADHEX(2) << +low_write_);
+					// as per register 7, but in blink mode.
+				break;
+
+				case 13:
+					LOG("TODO: Yamaha blink display times; " << PADHEX(2) << +low_write_);
+					// b0–b3: display time for odd page;
+					// b4–b7: display time for even page.
+				break;
+
+				case 14:
+					LOG("TODO: Yamaha A14–A16 selection; " << PADHEX(2) << +low_write_);
+					// b0–b2: A14–A16 of address counter (i.e. ram_pointer_)
+				break;
+
+				case 15:
 					Storage<personality>::selected_status_ = low_write_ & 0xf;
-				}
-			break;
+				break;
 
-			default:
-				LOG("Unknown TMS write: " << int(low_write_) << " to " << int(value));
-			break;
+				case 16:
+					LOG("TODO: Yamaha palette index selection; " << PADHEX(2) << +low_write_);
+					// b0–b3: palette entry for writing on port 2; autoincrements upon every write.
+				break;
+
+				case 17:
+					LOG("TODO: Yamaha indirect addressing; " << PADHEX(2) << +low_write_);
+					// b7: 1 = disable autoincrementing; 0 = enable.
+					// b5–b0: register number
+				break;
+
+				case 18:
+					LOG("TODO: Yamaha position adjustment; " << PADHEX(2) << +low_write_);
+					// b0-b3: horizontal adjustment
+					// b4-b7: vertical adjustment
+				break;
+
+				case 19:
+					LOG("TODO: Yamaha interrupt line; " << PADHEX(2) << +low_write_);
+					// b0–b7: line to match for interrupts (if eabled)
+				break;
+
+				case 20:
+				case 21:
+				case 22:
+					LOG("TODO: Yamaha colour burst selection; " << PADHEX(2) << +low_write_);
+					// Documentation is "fill with 0s for no colour burst; magic pattern for colour burst"
+				break;
+
+				case 23:
+					LOG("TODO: Yamaha vertical offset; " << PADHEX(2) << +low_write_);
+					// i.e. scrolling.
+				break;
+
+				case 32:
+				case 33:
+					LOG("TODO: Yamaha command source x; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 34:
+				case 35:
+					LOG("TODO: Yamaha command source y; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 36:
+				case 37:
+					LOG("TODO: Yamaha command destination x; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 38:
+				case 39:
+					LOG("TODO: Yamaha command destination y; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 40:
+				case 41:
+					LOG("TODO: Yamaha command size x; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 42:
+				case 43:
+					LOG("TODO: Yamaha command size y; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 44:
+					LOG("TODO: Yamaha command colour; " << PADHEX(2) << +low_write_);
+				break;
+
+				case 45:
+					LOG("TODO: Yamaha VRAM bank selection addressing and command arguments; " << PADHEX(2) << +low_write_);
+					// b6: 0 = video RAM; 1 = expandion RAM.
+					// b5: MXD (???)
+					// b4: MXS
+					// b3: DIY
+					// b2: DIX
+					// b1: EQ
+					// b0: MAJ
+				break;
+
+				case 46:
+					LOG("TODO: Yamaha command; " << PADHEX(2) << +low_write_);
+					// b0–b3: LO0–LO3 (???)
+					// b4–b7: CM0-CM3 (???)
+				break;
+			}
 		}
 	} else {
 		// This is an access via the RAM pointer.