diff --git a/src/devices/video/pc_vga_matrox.cpp b/src/devices/video/pc_vga_matrox.cpp
index ab43443a70b..20e9e5d8f5e 100644
--- a/src/devices/video/pc_vga_matrox.cpp
+++ b/src/devices/video/pc_vga_matrox.cpp
@@ -13,12 +13,15 @@ matrox_vga_device::matrox_vga_device(const machine_config &mconfig, const char *
 	// 3 bits of address space?
 	m_crtcext_space_config = address_space_config("crtcext_regs", ENDIANNESS_LITTLE, 8, 8, 0, address_map_constructor(FUNC(matrox_vga_device::crtcext_map), this));
 	// TODO: docs mentions using 0x22 / 0x24 / 0x26 for regular CRTC (coming from plain VGA?)
+
+	m_ramdac_indexed_space_config = address_space_config("ramdac_indexed_regs", ENDIANNESS_LITTLE, 8, 8, 0, address_map_constructor(FUNC(matrox_vga_device::ramdac_indexed_map), this));
 }
 
 device_memory_interface::space_config_vector matrox_vga_device::memory_space_config() const
 {
 	auto r = svga_device::memory_space_config();
-	r.emplace_back(std::make_pair(EXT_REG, &m_crtcext_space_config));
+	r.emplace_back(std::make_pair(EXT_REG,     &m_crtcext_space_config));
+	r.emplace_back(std::make_pair(EXT_REG + 1, &m_ramdac_indexed_space_config));
 	return r;
 }
 
@@ -27,6 +30,10 @@ void matrox_vga_device::device_reset()
 	svga_device::device_reset();
 
 	m_crtcext_index = 0;
+	m_crtcext_misc = 0;
+	m_mgamode = false;
+	m_truecolor_ctrl = 0x80;
+	m_multiplex_ctrl = 0x98;
 }
 
 void matrox_vga_device::io_3bx_3dx_map(address_map &map)
@@ -56,7 +63,7 @@ void matrox_vga_device::crtcext_map(address_map &map)
 //  map(0x00, 0x00) Address Generator Extensions
 //  map(0x01, 0x01) Horizontal Counter Extensions
 //  map(0x02, 0x02) Vertical Counter Extensions
-//  map(0x03, 0x03) Miscellaneous
+	map(0x03, 0x03).rw(FUNC(matrox_vga_device::crtcext3_misc_r), FUNC(matrox_vga_device::crtcext3_misc_w));
 //  CRTCEXT4 Memory Page register
 	map(0x04, 0x04).lrw8(
 		NAME([this] (offs_t offset) { return svga.bank_w & 0x7f; }),
@@ -68,53 +75,198 @@ void matrox_vga_device::crtcext_map(address_map &map)
 //     seems to disable SVGA drawing -> diagnostic check?
 }
 
+/*
+ * CRTCEXT3 Miscellaneous
+ *
+ * x--- ---- MGA mode (SVGA and accelerated modes)
+ * -x-- ---- CSYNCEN
+ * --x- ---- SLOW256 disables HW acceleration if '1' for VGA mode 13h
+ * ---x x--- VIDDELAY delay for CRTC signals, depends on RAM configuration
+ * ---0 0--- 4MB board
+ * ---0 1--- 2MB board
+ * ---1 x--- 8MB board
+ * ---- -xxx SCALE dot clock scaling factor
+ * ---- -000 /1
+ * ---- -001 /2
+ * ---- -010 /3
+ * ---- -011 /4
+ * ---- -100 <reserved>
+ * ---- -101 /6
+ * ---- -110 <reserved>
+ * ---- -111 /8
+ */
+u8 matrox_vga_device::crtcext3_misc_r()
+{
+	return m_crtcext_misc;
+}
+
+void matrox_vga_device::crtcext3_misc_w(offs_t offset, u8 data)
+{
+	logerror("CRTCEXT3: %02x\n", data);
+	m_crtcext_misc = data;
+	m_mgamode = bool(BIT(data, 7));
+}
+
 // RAMDAC
 // - paired with a Texas Instruments TVP3026 here -> a superset of INMOS IMSG176/IMSG178
 // - integrated with a superset in G400 at least
 void matrox_vga_device::ramdac_ext_map(address_map &map)
 {
-//	map(0x00, 0x00).rw(FUNC(matrox_vga_device::ramdac_write_index_r), FUNC(matrox_vga_device::ramdac_write_index_w));
-//	map(0x01, 0x01).rw(FUNC(matrox_vga_device::ramdac_data_r), FUNC(matrox_vga_device::ramdac_data_w));
-//	map(0x02, 0x02).rw(FUNC(matrox_vga_device::ramdac_mask_r), FUNC(matrox_vga_device::ramdac_mask_w));
-//	map(0x03, 0x03).rw(FUNC(matrox_vga_device::ramdac_read_index_r), FUNC(matrox_vga_device::ramdac_read_index_w));
-//	map(0x04, 0x04) Cursor/Overscan Color Write Index
-//	map(0x05, 0x05) Cursor/Overscan Color data
-//	map(0x07, 0x07) Cursor/Overscan Color Read Index
-//	map(0x09, 0x09) Direct Cursor control
+//  map(0x00, 0x00).rw(FUNC(matrox_vga_device::ramdac_write_index_r), FUNC(matrox_vga_device::ramdac_write_index_w));
+//  map(0x01, 0x01).rw(FUNC(matrox_vga_device::ramdac_data_r), FUNC(matrox_vga_device::ramdac_data_w));
+//  map(0x02, 0x02).rw(FUNC(matrox_vga_device::ramdac_mask_r), FUNC(matrox_vga_device::ramdac_mask_w));
+//  map(0x03, 0x03).rw(FUNC(matrox_vga_device::ramdac_read_index_r), FUNC(matrox_vga_device::ramdac_read_index_w));
+//  map(0x04, 0x04) Cursor/Overscan Color Write Index
+//  map(0x05, 0x05) Cursor/Overscan Color data
+//  map(0x07, 0x07) Cursor/Overscan Color Read Index
+//  map(0x09, 0x09) Direct Cursor control
 	map(0x0a, 0x0a).rw(FUNC(matrox_vga_device::ramdac_ext_indexed_r), FUNC(matrox_vga_device::ramdac_ext_indexed_w));
-//	map(0x0b, 0x0b) Cursor RAM data
-//	map(0x0c, 0x0f) Cursor X/Y positions
-//	map(0x10, 0x1f) <reserved>
+//  map(0x0b, 0x0b) Cursor RAM data
+//  map(0x0c, 0x0f) Cursor X/Y positions
+//  map(0x10, 0x1f) <reserved>
 }
 
 u8 matrox_vga_device::ramdac_ext_indexed_r()
 {
 	// Unclear from the docs, according to usage seems to be the write index with no autoincrement
-	logerror("RAMDAC ext read [%02x]++\n", vga.dac.write_index);
-	return m_ramdac_mode;
+	logerror("RAMDAC ext read [%02x]\n", vga.dac.write_index);
+	return space(EXT_REG + 1).read_byte(vga.dac.write_index);
+;
 }
 
 void matrox_vga_device::ramdac_ext_indexed_w(offs_t offset, u8 data)
 {
-	// TODO: really uses the palette write index, cheating for now
-	m_ramdac_mode = data;
-	logerror("RAMDAC ext [%02x]++ %02x\n", vga.dac.write_index, data);
-	if (!machine().side_effects_disabled())
-		vga.dac.write_index ++;
-	svga.rgb16_en = (data & 0xf8) == 0xf0;
+	logerror("RAMDAC ext [%02x] %02x\n", vga.dac.write_index, data);
+	space(EXT_REG + 1).write_byte(vga.dac.write_index, data);
+}
+
+void matrox_vga_device::ramdac_indexed_map(address_map &map)
+{
+	map(0x18, 0x18).rw(FUNC(matrox_vga_device::truecolor_ctrl_r), FUNC(matrox_vga_device::truecolor_ctrl_w));
+	map(0x19, 0x19).rw(FUNC(matrox_vga_device::multiplex_ctrl_r), FUNC(matrox_vga_device::multiplex_ctrl_w));
+}
+
+u8 matrox_vga_device::truecolor_ctrl_r()
+{
+	return m_truecolor_ctrl;
+}
+
+void matrox_vga_device::truecolor_ctrl_w(offs_t offset, u8 data)
+{
+	m_truecolor_ctrl = data;
+	flush_true_color_mode();
+}
+
+u8 matrox_vga_device::multiplex_ctrl_r()
+{
+	return m_multiplex_ctrl;
+}
+
+void matrox_vga_device::multiplex_ctrl_w(offs_t offset, u8 data)
+{
+	m_multiplex_ctrl = data;
+	flush_true_color_mode();
+}
+
+void matrox_vga_device::flush_true_color_mode()
+{
+	logerror("New video mode %02x %02x\n", m_truecolor_ctrl, m_multiplex_ctrl);
+	svga.rgb8_en = svga.rgb15_en = svga.rgb16_en = svga.rgb24_en = svga.rgb32_en = 0;
+	if (m_truecolor_ctrl == 0x80 && m_multiplex_ctrl == 0x98)
+	{
+		logerror("\tVGA mode\n");
+		return;
+	}
+
+	switch(m_truecolor_ctrl)
+	{
+		case 0x80:
+			if (m_multiplex_ctrl >= 0x49 && m_multiplex_ctrl <= 0x4c)
+			{
+				logerror("\tSVGA 8-bit mode\n");
+				svga.rgb8_en = 1;
+			}
+			else
+			{
+				// [0x41, 0x42, 0x43, 0x44] for normal
+				// [0x61, 0x62, 0x63, 0x64] for nibble swapped
+				popmessage("TVP3026: Unemulated 4-bit %s with multiplex: %02x"
+					, m_multiplex_ctrl & 0x20 ? "normal" : "nibble swapped"
+					, m_multiplex_ctrl
+				);
+			}
+			break;
+		case 0x16:
+		case 0x1e:
+		case 0x56:
+		case 0x5e:
+			if (m_multiplex_ctrl == 0x5b || m_multiplex_ctrl == 0x5c)
+			{
+				logerror("\tRGB 8-8-8 mode\n");
+				svga.rgb24_en = 1;
+			}
+			break;
+		case 0x17:
+		case 0x1f:
+		case 0x57:
+		case 0x5f:
+			if (m_multiplex_ctrl == 0x5b || m_multiplex_ctrl == 0x5c)
+				popmessage("TVP3026: Unemulated BGR 8-8-8 mode");
+			break;
+		case 0x06:
+		case 0x46:
+			if (m_multiplex_ctrl == 0x5b || m_multiplex_ctrl == 0x5c)
+			{
+				logerror("\t%cRGB 8-8-8-8 mode\n", m_truecolor_ctrl & 0x40 ? "X" : "O");
+				svga.rgb32_en = 1;
+			}
+			break;
+		case 0x07:
+		case 0x47:
+			if (m_multiplex_ctrl == 0x5b || m_multiplex_ctrl == 0x5c)
+				popmessage("TVP3026: Unemulated BGR%c 8-8-8-8 mode", m_truecolor_ctrl & 0x40 ? "X" : "O");
+			break;
+		case 0x05:
+		case 0x45:
+			if (m_multiplex_ctrl >= 0x52 && m_multiplex_ctrl <= 0x54)
+			{
+				logerror("\tXGA RGB 5-6-5 mode\n");
+				svga.rgb16_en = 1;
+			}
+			break;
+		case 0x04:
+		case 0x44:
+			// 0x04 is selected by VESA 2.4 test, which may be buggy?
+			// (extended mode 110h, while above uses 111h)
+			if (m_multiplex_ctrl >= 0x52 && m_multiplex_ctrl <= 0x54)
+			{
+				logerror("\tTarga %cRGB 1-5-5-5 mode\n", m_truecolor_ctrl & 0x40 ? "X" : "O");
+				svga.rgb16_en = 1;
+			}
+			break;
+		case 0x03:
+		case 0x43:
+			if (m_multiplex_ctrl >= 0x52 && m_multiplex_ctrl <= 0x54)
+				popmessage("TVP3026: Unemulated RGB 6-6-4 mode");
+			break;
+		case 0x01:
+		case 0x41:
+			if (m_multiplex_ctrl >= 0x52 && m_multiplex_ctrl <= 0x54)
+				popmessage("TVP3026: Unemulated RGB%c 4-4-4-4 mode", m_truecolor_ctrl & 0x40 ? "X" : "O");
+			break;
+	}
 }
 
 uint8_t matrox_vga_device::mem_r(offs_t offset)
 {
-	// TODO: MGA mode CRTCEXT3 bit 7
-	if (svga.rgb16_en)
+	if (m_mgamode)
 		return svga_device::mem_linear_r(offset + (svga.bank_w * 0x10000));
 	return svga_device::mem_r(offset);
 }
 
 void matrox_vga_device::mem_w(offs_t offset, uint8_t data)
 {
-	if (svga.rgb16_en)
+	if (m_mgamode)
 	{
 		svga_device::mem_linear_w(offset + (svga.bank_w * 0x10000), data);
 		return;
diff --git a/src/devices/video/pc_vga_matrox.h b/src/devices/video/pc_vga_matrox.h
index 295253c45c1..b6cbc14fc31 100644
--- a/src/devices/video/pc_vga_matrox.h
+++ b/src/devices/video/pc_vga_matrox.h
@@ -24,17 +24,36 @@ protected:
 
 	virtual void device_reset() override;
 
-	void crtcext_map(address_map &map);
 	virtual uint16_t offset() override;
+
+	void crtcext_map(address_map &map);
+	void ramdac_indexed_map(address_map &map);
+	void flush_true_color_mode();
 private:
 	virtual space_config_vector memory_space_config() const override;
 
 	address_space_config m_crtcext_space_config;
+	address_space_config m_ramdac_indexed_space_config;
+
+	// CRTC
+	u8 crtcext3_misc_r();
+	void crtcext3_misc_w(offs_t offset, u8 data);
+	u8 m_crtcext_index = 0;
+
+	u8 m_crtcext_misc = 0;
+	bool m_mgamode = false;
+
+	// RAMDAC
 	u8 ramdac_ext_indexed_r();
 	void ramdac_ext_indexed_w(offs_t offset, u8 data);
 
-	u8 m_crtcext_index = 0;
-	u8 m_ramdac_mode = 0;
+	u8 truecolor_ctrl_r();
+	void truecolor_ctrl_w(offs_t offset, u8 data);
+	u8 multiplex_ctrl_r();
+	void multiplex_ctrl_w(offs_t offset, u8 data);
+
+	u8 m_multiplex_ctrl = 0;
+	u8 m_truecolor_ctrl = 0;
 };
 
 DECLARE_DEVICE_TYPE(MATROX_VGA, matrox_vga_device)