Add DEX and DEY instructions

src/6502/6502.h

@@ -41,6 +41,9 @@ typedef unsigned short word; // 16 bit
 #define INS_INX 0xE8 // INX Implied
 #define INS_INY 0xC8 // INY Implied
 
+#define INS_DEX 0xCA // DEX Implied
+#define INS_DEY 0x88 // DEY Implied
+
 struct MEMORY {
 	byte memory[MAX_MEMORY];
 };

src/6502/main.c

@@ -175,6 +175,7 @@ void execute() {
 				break;
 		        case INS_NOP:
 			        break;
+				
          		case INS_INX:
 			        cpu.X++;
 			        cpu.Z = (cpu.X == 0);
@@ -185,6 +186,17 @@ void execute() {
 			        cpu.Z = (cpu.Y == 0);
 				cpu.N = (cpu.Y & 0b1000000) > 0;
 			        break;
+
+		        case INS_DEX:
+			        cpu.X--;
+			        cpu.Z = (cpu.X == 0);
+				cpu.N = (cpu.X & 0b1000000) > 0;
+			        break;
+		        case INS_DEY:
+			        cpu.Y--;
+			        cpu.Z = (cpu.Y == 0);
+				cpu.N = (cpu.Y & 0b1000000) > 0;
+			        break;
 		        case 0x00: // EOF
 			        return;
 			default: