diff --git a/src/devices/cpu/m6800/6800dasm.cpp b/src/devices/cpu/m6800/6800dasm.cpp
index 49f908013cd..2e94ef3b62d 100644
--- a/src/devices/cpu/m6800/6800dasm.cpp
+++ b/src/devices/cpu/m6800/6800dasm.cpp
@@ -52,7 +52,8 @@ enum op_names {
 	rts,    sba,    sbca,   sbcb,   sec,    sev,    sta,    stb,
 	_std,   sei,    sts,    stx,    suba,   subb,   subd,   swi,
 	wai,    tab,    tap,    tba,    tim,    tpa,    tst,    tsta,
-	tstb,   tsx,    txs,    asx1,   asx2,   xgdx,   addx,   adcx
+	tstb,   tsx,    txs,    asx1,   asx2,   xgdx,   addx,   adcx,
+	bitx
 };
 
 static const char *const op_name_str[] = {
@@ -71,7 +72,8 @@ static const char *const op_name_str[] = {
 	"rts",   "sba",   "sbca",  "sbcb",  "sec",   "sev",   "sta",   "stb",
 	"std",   "sei",   "sts",   "stx",   "suba",  "subb",  "subd",  "swi",
 	"wai",   "tab",   "tap",   "tba",   "tim",   "tpa",   "tst",   "tsta",
-	"tstb",  "tsx",   "txs",   "asx1",  "asx2",  "xgdx",  "addx",  "adcx"
+	"tstb",  "tsx",   "txs",   "asx1",  "asx2",  "xgdx",  "addx",  "adcx",
+	"bitx"
 };
 
 /*
@@ -82,7 +84,7 @@ static const char *const op_name_str[] = {
  * 2    invalid opcode for 1:6800/6802/6808, 2:6801/6803, 4:HD63701
  */
 
-static const UINT8 table[0x102][3] = {
+static const UINT8 table[0x104][3] = {
 	{ill, inh,7},{nop, inh,0},{ill, inh,7},{ill, inh,7},/* 00 */
 	{lsrd,inh,1},{asld,inh,1},{tap, inh,0},{tpa, inh,0},
 	{inx, inh,0},{dex, inh,0},{clv, inh,0},{sev, inh,0},
@@ -151,7 +153,11 @@ static const UINT8 table[0x102][3] = {
 	/* extra instruction $fc for NSC-8105 */
 	{addx,ext,0},
 	/* extra instruction $ec for NSC-8105 */
-	{adcx,imb,0}
+	{adcx,imb,0},
+	/* extra instruction $bb for NSC-8105 */
+	{bitx,imx,0},
+	/* extra instruction $b2 for NSC-8105 */
+	{stx,imx,0}
 };
 
 /* some macros to keep things short */
@@ -188,6 +194,8 @@ static unsigned Dasm680x (int subtype, char *buf, unsigned pc, const UINT8 *opro
 		/* and check for extra instruction */
 		if (code == 0xfc)  code = 0x0100;
 		if (code == 0xec)  code = 0x0101;
+		if (code == 0x7b) code = 0x0102;
+		if (code == 0x71) code = 0x0103;
 	}
 
 	opcode = table[code][0];
diff --git a/src/devices/cpu/m6800/6800ops.inc b/src/devices/cpu/m6800/6800ops.inc
index 4e92e401be7..078529d16ab 100644
--- a/src/devices/cpu/m6800/6800ops.inc
+++ b/src/devices/cpu/m6800/6800ops.inc
@@ -2285,17 +2285,18 @@ OP_HANDLER( stx_ex )
 }
 
 /* NSC8105 specific, guessed opcodes (tested by Night Gal Summer) */
-// $bb - load A from [X + $0]
-OP_HANDLER( ldax_imm )
+// $bb - $mask & [X + $disp8]
+OP_HANDLER( btst_ix )
 {
 	UINT8 val;
-	{EA=X+((M_RDOP_ARG(PCD)<<8) | M_RDOP_ARG((PCD+1)&0xffff));PC+=2;}
-	val = RM(EAD);
+	UINT8 mask = M_RDOP_ARG(PCD);
+	{EA=X+(M_RDOP_ARG(PCD+1));PC+=2;}
+	val = RM(EAD) & mask;
 	CLR_NZVC; SET_NZ8(val);
 }
 
 // $b2 - assuming correct, store first byte to (X + $disp8)
-OP_HANDLER( nsc_unk )
+OP_HANDLER( stx_nsc )
 {
 	IMM8;
 	UINT8 val = RM(EAD);
@@ -2304,13 +2305,4 @@ OP_HANDLER( nsc_unk )
 	CLR_NZV;
 	SET_NZ8(val);
 	WM(EAD,val);
-}
-
-// $00 - store A to [X + $0]
-OP_HANDLER( stax_imm )
-{
-	CLR_NZV;
-	SET_NZ8(A);
-	EA=X;
-	WM(EAD,A);
 }
\ No newline at end of file
diff --git a/src/devices/cpu/m6800/6800tbl.inc b/src/devices/cpu/m6800/6800tbl.inc
index 266ddb2a55c..10515e54bdc 100644
--- a/src/devices/cpu/m6800/6800tbl.inc
+++ b/src/devices/cpu/m6800/6800tbl.inc
@@ -106,7 +106,7 @@ const m6800_cpu_device::op_func m6800_cpu_device::hd63701_insn[0x100] = {
 
 const m6800_cpu_device::op_func m6800_cpu_device::nsc8105_insn[0x100] = {
 // 0
-&m6800_cpu_device::stax_imm,&m6800_cpu_device::illegal,&m6800_cpu_device::nop,    &m6800_cpu_device::illegal,&m6800_cpu_device::illegal,&m6800_cpu_device::tap,    &m6800_cpu_device::illegal,&m6800_cpu_device::tpa,
+&m6800_cpu_device::illegal,&m6800_cpu_device::illegal,&m6800_cpu_device::nop,    &m6800_cpu_device::illegal,&m6800_cpu_device::illegal,&m6800_cpu_device::tap,    &m6800_cpu_device::illegal,&m6800_cpu_device::tpa,
 // 8
 &m6800_cpu_device::inx,    &m6800_cpu_device::clv,    &m6800_cpu_device::dex,    &m6800_cpu_device::sev,    &m6800_cpu_device::clc,    &m6800_cpu_device::cli,    &m6800_cpu_device::sec,    &m6800_cpu_device::sei,
 // 10
@@ -150,9 +150,9 @@ const m6800_cpu_device::op_func m6800_cpu_device::nsc8105_insn[0x100] = {
 // a8
 &m6800_cpu_device::asl_ix, &m6800_cpu_device::dec_ix, &m6800_cpu_device::rol_ix, &m6800_cpu_device::illegal,&m6800_cpu_device::inc_ix, &m6800_cpu_device::jmp_ix, &m6800_cpu_device::tst_ix, &m6800_cpu_device::clr_ix,
 // b0
-&m6800_cpu_device::neg_ex, &m6800_cpu_device::illegal,&m6800_cpu_device::nsc_unk,&m6800_cpu_device::com_ex, &m6800_cpu_device::lsr_ex, &m6800_cpu_device::ror_ex, &m6800_cpu_device::illegal,&m6800_cpu_device::asr_ex,
+&m6800_cpu_device::neg_ex, &m6800_cpu_device::illegal,&m6800_cpu_device::stx_nsc,&m6800_cpu_device::com_ex, &m6800_cpu_device::lsr_ex, &m6800_cpu_device::ror_ex, &m6800_cpu_device::illegal,&m6800_cpu_device::asr_ex,
 // b8
-&m6800_cpu_device::asl_ex, &m6800_cpu_device::dec_ex, &m6800_cpu_device::rol_ex, &m6800_cpu_device::ldax_imm,&m6800_cpu_device::inc_ex, &m6800_cpu_device::jmp_ex, &m6800_cpu_device::tst_ex, &m6800_cpu_device::clr_ex,
+&m6800_cpu_device::asl_ex, &m6800_cpu_device::dec_ex, &m6800_cpu_device::rol_ex, &m6800_cpu_device::btst_ix,&m6800_cpu_device::inc_ex, &m6800_cpu_device::jmp_ex, &m6800_cpu_device::tst_ex, &m6800_cpu_device::clr_ex,
 &m6800_cpu_device::subb_im,&m6800_cpu_device::sbcb_im,&m6800_cpu_device::cmpb_im,&m6800_cpu_device::illegal,&m6800_cpu_device::andb_im,&m6800_cpu_device::ldb_im, &m6800_cpu_device::bitb_im,&m6800_cpu_device::stb_im,
 &m6800_cpu_device::eorb_im,&m6800_cpu_device::orb_im, &m6800_cpu_device::adcb_im,&m6800_cpu_device::addb_im,&m6800_cpu_device::illegal,&m6800_cpu_device::ldx_im, &m6800_cpu_device::illegal,&m6800_cpu_device::stx_im,
 &m6800_cpu_device::subb_di,&m6800_cpu_device::sbcb_di,&m6800_cpu_device::cmpb_di,&m6800_cpu_device::illegal,&m6800_cpu_device::andb_di,&m6800_cpu_device::ldb_di, &m6800_cpu_device::bitb_di,&m6800_cpu_device::stb_di,
diff --git a/src/devices/cpu/m6800/m6800.h b/src/devices/cpu/m6800/m6800.h
index 6ddffe64242..82696a6ee43 100644
--- a/src/devices/cpu/m6800/m6800.h
+++ b/src/devices/cpu/m6800/m6800.h
@@ -426,9 +426,8 @@ protected:
 	void cpx_im();
 	void cpx_ix();
 	void trap();
-	void ldax_imm();
-	void stax_imm();
-	void nsc_unk();
+	void btst_ix();
+	void stx_nsc();
 };
 
 
diff --git a/src/mame/drivers/nightgal.cpp b/src/mame/drivers/nightgal.cpp
index d11900aa822..736059fbc05 100644
--- a/src/mame/drivers/nightgal.cpp
+++ b/src/mame/drivers/nightgal.cpp
@@ -87,7 +87,6 @@ public:
 	DECLARE_DRIVER_INIT(ngalsumr);
 	DECLARE_DRIVER_INIT(royalqn);
 	DECLARE_WRITE8_MEMBER(ngalsumr_unk_w);
-	DECLARE_READ8_MEMBER(ngalsumr_color_r);
 	virtual void machine_start() override;
 	virtual void machine_reset() override;
 	virtual void video_start() override;
@@ -1099,17 +1098,10 @@ WRITE8_MEMBER(nightgal_state::ngalsumr_unk_w)
 	//m_z80_latch = data;
 }
 
-// check with the unknown opcode, maybe it actually just masks with first parameter and second one is displacement byte offset?
-READ8_MEMBER(nightgal_state::ngalsumr_color_r)
-{
-	return (m_comms_ram[offset] & 0x80);
-}
-
 DRIVER_INIT_MEMBER(nightgal_state,ngalsumr)
 {
 	m_maincpu->space(AS_PROGRAM).install_write_handler(0x6000, 0x6000, write8_delegate(FUNC(nightgal_state::ngalsumr_unk_w), this) );
 	// 0x6003 some kind of f/f state
-	m_subcpu->space(AS_PROGRAM).install_read_handler(0x9000, 0x903f, read8_delegate(FUNC(nightgal_state::ngalsumr_color_r),this) );
 }
 
 /* Type 1 HW */