diff --git a/src/emu/cpu/sm510/sm510.c b/src/emu/cpu/sm510/sm510.c
index c428eb76e40..09029709849 100644
--- a/src/emu/cpu/sm510/sm510.c
+++ b/src/emu/cpu/sm510/sm510.c
@@ -8,7 +8,7 @@
   - SM512: 4Kx8 ROM, 128x4 RAM(48x4 for LCD), melody controller
   
   Other chips that may be in the same family, investigate more when one of
-  them needs to get emulated: SM500, SM530, SM531, ..
+  them needs to get emulated: SM500, SM530/31, SM4A, SM3903, ..
 
   References:
   - 1990 Sharp Microcomputers Data Book
diff --git a/src/emu/cpu/sm510/sm510op.c b/src/emu/cpu/sm510/sm510op.c
index 91dd26d1ccb..bb0f4975511 100644
--- a/src/emu/cpu/sm510/sm510op.c
+++ b/src/emu/cpu/sm510/sm510op.c
@@ -57,10 +57,22 @@ inline UINT8 sm510_base_device::bitmask(UINT16 param)
 void sm510_base_device::op_lb()
 {
 	// LB x: load BM/BL with 4-bit immediate value (partial)
+	
+	// SM510 WIP..
+	// bm and bl(low) are probably ok!
 	m_bm = (m_bm & 4) | (m_op & 3);
-	m_bl = m_op >> 2 & 3;
-	if (m_bl == 3)
-		m_bl |= 0xc;
+	m_bl = (m_op >> 2 & 3);
+	
+	// bl(high) is still unclear, official doc is confusing
+	UINT8 hi = 0;
+	switch (m_bl)
+	{
+		case 0: hi = 3; break;
+		case 1: hi = 0; break;
+		case 2: hi = 0; break;
+		case 3: hi = 3; break;
+	}
+	m_bl |= (hi << 2 & 0xc);
 }
 
 void sm510_base_device::op_lbl()