diff --git a/src/mess/drivers/thomson.c b/src/mess/drivers/thomson.c
index c5c26accad1..696ab3ed17a 100644
--- a/src/mess/drivers/thomson.c
+++ b/src/mess/drivers/thomson.c
@@ -1091,6 +1091,9 @@ static MACHINE_CONFIG_DERIVED( mo5, to7 )
 
 	MCFG_DEVICE_REMOVE( "mc6846" )
 
+       MCFG_PALETTE_MODIFY( "palette" )
+	MCFG_PALETTE_INIT_OWNER(thomson_state, mo5)
+
 	MCFG_DEVICE_MODIFY(THOM_PIA_SYS)
 	MCFG_PIA_READPA_HANDLER(READ8(thomson_state, mo5_sys_porta_in))
 	MCFG_PIA_READPB_HANDLER(READ8(thomson_state, mo5_sys_portb_in))
diff --git a/src/mess/includes/thomson.h b/src/mess/includes/thomson.h
index d81f71a633f..3e2848ed692 100644
--- a/src/mess/includes/thomson.h
+++ b/src/mess/includes/thomson.h
@@ -259,6 +259,7 @@ public:
 	void to9_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap4_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap4alt_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
+	void bitmap4althalf_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap16_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void mode80_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void mode80_to9_scandraw_16( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
@@ -271,6 +272,7 @@ public:
 	void to9_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap4_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap4alt_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
+	void bitmap4althalf_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void bitmap16_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void mode80_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
 	void mode80_to9_scandraw_8( UINT8* vram, UINT16* dst, UINT16* pal, int org, int len );
@@ -306,6 +308,7 @@ public:
 	WRITE_LINE_MEMBER( fdc_index_3_w );
 	void thomson_index_callback(legacy_floppy_image_device *device, int state);
 	DECLARE_PALETTE_INIT(thom);
+	DECLARE_PALETTE_INIT(mo5);
 
 	optional_device<mc6854_device> m_mc6854;
 
@@ -519,6 +522,7 @@ protected:
 	void thom_set_mode_point( int point );
 	void thom_floppy_active( int write );
 	unsigned to7_lightpen_gpl( int decx, int decy );
+	void thom_configure_palette( double gamma, const UINT16* pal, palette_device& palette );
 
 	int thom_floppy_make_addr( chrn_id id, UINT8* dst, int sector_size );
 	int thom_floppy_make_sector( legacy_floppy_image_device* img, chrn_id id, UINT8* dst, int sector_size );
@@ -602,7 +606,8 @@ protected:
 #define THOM_VMODE_OVERLAY3    9
 #define THOM_VMODE_TO9        10
 #define THOM_VMODE_80_TO9     11
-#define THOM_VMODE_NB         12
+#define THOM_VMODE_BITMAP4_ALT_HALF 12
+#define THOM_VMODE_NB         13
 
 
 class to7_io_line_device : public device_t
diff --git a/src/mess/machine/thomson.c b/src/mess/machine/thomson.c
index de5e6a9c8ac..77a94351778 100644
--- a/src/mess/machine/thomson.c
+++ b/src/mess/machine/thomson.c
@@ -2039,10 +2039,16 @@ void thomson_state::to9_set_video_mode( UINT8 data, int style )
 			thom_set_video_mode( THOM_VMODE_TO9 );
 		break;
 
+        // undocumented, but tested on a real TO8D
+        case 0x20: thom_set_video_mode( THOM_VMODE_MO5 );         break;
+
 	case 0x21: thom_set_video_mode( THOM_VMODE_BITMAP4 );     break;
 
 	case 0x41: thom_set_video_mode( THOM_VMODE_BITMAP4_ALT ); break;
 
+        // also undocumented but tested
+	case 0x59: thom_set_video_mode( THOM_VMODE_BITMAP4_ALT_HALF ); break;
+
 	case 0x2a:
 		if ( style==0 )
 			thom_set_video_mode( THOM_VMODE_80_TO9 );
@@ -2110,7 +2116,6 @@ WRITE8_MEMBER( thomson_state::to9_vreg_w )
 		color = m_to9_palette_data[ 2 * idx + 1 ];
 		color = m_to9_palette_data[ 2 * idx ] | (color << 8);
 		thom_set_palette( idx ^ 8, color & 0x1fff );
-
 		m_to9_palette_idx = ( m_to9_palette_idx + 1 ) & 31;
 	}
 	break;
diff --git a/src/mess/video/thomson.c b/src/mess/video/thomson.c
index 398aa208519..90ffd6675d7 100644
--- a/src/mess/video/thomson.c
+++ b/src/mess/video/thomson.c
@@ -495,6 +495,29 @@ UPDATE_LOW( bitmap4alt )
 END_UPDATE
 
 
+/* 160x200, 4 colors, no constraint, using only one memory page (undocumented) */
+
+UPDATE_HI( bitmap4althalf )
+{
+	dst[ 0] = dst[ 1] = dst[ 2] = dst[ 3] = pal[ rama >> 6 ];
+	dst[ 4] = dst[ 5] = dst[ 6] = dst[ 7] = pal[ (rama >> 4) & 3 ];
+	dst[ 8] = dst[ 9] = dst[10] = dst[11] = pal[ (rama >> 2) & 3];
+	dst[12] = dst[13] = dst[14] = dst[15] = pal[ rama & 3 ];
+	(void)ramb; // ramb is not used
+}
+END_UPDATE
+
+UPDATE_LOW( bitmap4althalf )
+{
+	dst[0] = dst[1] = pal[ rama >> 6 ];
+	dst[2] = dst[3] = pal[ (rama >> 4) & 3 ];
+	dst[4] = dst[5] = pal[ (rama >> 2) & 3];
+	dst[6] = dst[7] = pal[ rama & 3 ];
+	(void)ramb; // ramb is not used
+}
+END_UPDATE
+
+
 
 /* 160x200, 16-colors, no constraint */
 
@@ -702,6 +725,7 @@ static const thom_scandraw thom_scandraw_funcs[THOM_VMODE_NB][2] =
 	FUN(to770),    FUN(mo5),    FUN(bitmap4), FUN(bitmap4alt),  FUN(mode80),
 	FUN(bitmap16), FUN(page1),  FUN(page2),   FUN(overlay),     FUN(overlay3),
 	FUN(to9), FUN(mode80_to9),
+        FUN(bitmap4althalf),
 };
 
 
@@ -1002,7 +1026,10 @@ void thomson_state::thom_vblank( screen_device &screen, bool state )
 /* -------------- initialization --------------- */
 
 
-
+/* TO7, TO7/70 palette, hardcoded in ROM
+   without further information, we assume that the hardcoded values
+   are the same as those setup by the TO8/TO9+/MO6 when booting up
+ */
 static const UINT16 thom_pal_init[16] =
 {
 	0x1000, /* 0: black */        0x000f, /* 1: red */
@@ -1012,9 +1039,23 @@ static const UINT16 thom_pal_init[16] =
 	0x0777, /* 8: gray */         0x033a, /* 9: pink */
 	0x03a3, /* a: light green */  0x03aa, /* b: light yellow */
 	0x0a33, /* c: light blue */   0x0a3a, /* d: redish pink */
-	0x0ee7, /* e: light cyan */   0x003b, /* f: orange */
+	0x0ee7, /* e: light cyan */   0x007b, /* f: orange */
 };
 
+/* MO5 palette, hardcoded in a ROM
+   values are from "Manuel Technique du MO5", p.19
+ */
+static const UINT16 mo5_pal_init[16] =
+{
+	0x1000, /* 0: black */        0x055f, /* 1: red */
+	0x00f0, /* 2: geen */         0x00ff, /* 3: yellow */
+	0x0f55, /* 4: blue */         0x0f0f, /* 5: purple */
+	0x0ff5, /* 6: cyan */         0x0fff, /* 7: white */
+	0x0aaa, /* 8: gray */         0x0aaf, /* 9: pink */
+	0x0afa, /* a: light green */  0x0aff, /* b: light yellow */
+	0x0fa5, /* c: light blue */   0x0faf, /* d: parama pink */
+	0x0ffa, /* e: light cyan */   0x05af, /* f: orange */
+};
 
 
 VIDEO_START_MEMBER( thomson_state, thom )
@@ -1022,8 +1063,6 @@ VIDEO_START_MEMBER( thomson_state, thom )
 	LOG (( "thom: video start called\n" ));
 
 	/* scan-line state */
-	memcpy( m_thom_last_pal, thom_pal_init, 32 );
-	memcpy( m_thom_pal, thom_pal_init, 32 );
 	memset( m_thom_border_l, 0xff, sizeof( m_thom_border_l ) );
 	memset( m_thom_border_r, 0xff, sizeof( m_thom_border_r ) );
 	memset( m_thom_vbody, 0, sizeof( m_thom_vbody ) );
@@ -1082,15 +1121,13 @@ VIDEO_START_MEMBER( thomson_state, thom )
 }
 
 
-
-PALETTE_INIT_MEMBER(thomson_state, thom)
+/* sets the fixed palette (for MO5,TO7,TO7/70) and gamma correction */
+void thomson_state::thom_configure_palette(double gamma, const UINT16* pal, palette_device& palette)
 {
-	double gamma = 0.6f;
-	unsigned i;
+	memcpy( m_thom_last_pal, pal, 32 );
+	memcpy( m_thom_pal, pal, 32 );
 
-	LOG (( "thom: palette init called\n" ));
-
-	for ( i = 0; i < 4097; i++ )
+	for ( int i = 0; i < 4097; i++ )
 	{
 		UINT8 r = 255. * pow( (i & 15) / 15., gamma );
 		UINT8 g = 255. * pow( ((i>> 4) & 15) / 15., gamma );
@@ -1101,6 +1138,34 @@ PALETTE_INIT_MEMBER(thomson_state, thom)
 }
 
 
+PALETTE_INIT_MEMBER(thomson_state, thom)
+{
+	LOG (( "thom: palette init called\n" ));
+
+        /* TO8 and later use an EF9369 color palette chip
+           The spec shows a built-in gamma correction for gamma=2.8
+           i.e., output is out = in ^ (1/2.8)
+
+           For the TO7, the gamma correction is irrelevant.
+           
+           For the TO7/70, we use the same palette and gamma has the TO8,
+           which gives good results (but is not verified).
+         */
+        thom_configure_palette(1.0 / 2.8, thom_pal_init, palette);
+}
+
+PALETTE_INIT_MEMBER(thomson_state, mo5)
+{
+	LOG (( "thom: MO5 palette init called\n" ));
+
+        /* The MO5 has a different fixed palette than the TO7/70.
+           We use a smaller gamma correction which gives intutively better
+           results (but is not verified).
+         */
+        thom_configure_palette(1.0, mo5_pal_init, palette);
+}
+
+
 
 /***************************** TO7 / T9000 *************************/