SM511: small update to divider

src/devices/cpu/sm510/sm510.cpp

@@ -22,7 +22,7 @@
   - SM511 undocumented/guessed opcodes:
     * $01 is guessed as DIV to ACC transfer, unknown which bits
     * $5d is certainly CEND
-    * $65 is certainly IDIV, but not sure if it behaves same as on SM510
+    * $65 is certainly divider reset, but not sure if it behaves same as on SM510
 
 */
 
@@ -144,6 +144,7 @@ void sm510_base_device::device_start()
 
 void sm510_base_device::device_reset()
 {
+	// ACL
 	m_skip = false;
 	m_halt = false;
 	m_op = m_prev_op = 0;
@@ -317,7 +318,7 @@ TIMER_CALLBACK_MEMBER(sm510_base_device::div_timer_cb)
 {
 	m_div = (m_div + 1) & 0x7fff;
 
-	// 1S signal on overflow(falling edge of f1)
+	// 1S signal on overflow(falling edge of F1)
 	if (m_div == 0)
 		m_1s = true;
 

src/devices/cpu/sm510/sm510.h

@@ -284,6 +284,7 @@ protected:
 	void op_skip();
 	void op_cend();
 	void op_idiv();
+	void op_dr();
 	void op_dta();
 
 	void op_illegal();

src/devices/cpu/sm510/sm510op.cpp

@@ -450,10 +450,16 @@ void sm510_base_device::op_idiv()
 	m_div = 0;
 }
 
+void sm510_base_device::op_dr()
+{
+	// DR: reset divider low 8 bits
+	m_div &= 0x7f;
+}
+
 void sm510_base_device::op_dta()
 {
-	// DTA: transfer divider low bits to ACC
-	m_acc = BITSWAP16(m_div,0,0,0,0, 0,0,0,0, 0,0,0,0, 7,8,9,10) & 0xf;
+	// DTA: transfer divider low 4 bits to ACC
+	m_acc = BITSWAP16(m_div,0,0,0,0, 0,0,0,0, 0,0,0,0, 14,13,12,11) & 0xf;
 }
 
 void sm510_base_device::op_illegal()

src/devices/cpu/sm510/sm511core.cpp

@@ -127,7 +127,7 @@ void sm511_device::execute_one()
 		case 0x62: op_wr(); break;
 		case 0x63: op_ws(); break;
 		case 0x64: op_incb(); break;
-		case 0x65: op_idiv(); break;
+		case 0x65: op_dr(); break; // guessed
 		case 0x66: op_rc(); break;
 		case 0x67: op_sc(); break;
 		case 0x6c: op_decb(); break;