Added ALU and the ADC op code.

src/chip/MOS6502/cpu.js

 
 
 function ADC(cpu){
-
+  switch(cpu.__step){
+    case 0:
+      cpu.__mem.address = cpu.__PC;
+      PCUp(cpu, 1);
+      cpu.__opv = cpu.__mem.byte;
+      if (cpu.__op == 0x69){ // Immediate
+          cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__opv);
+          cpu.__op = -1; break;
+      }
+    case 1:
+      switch (cpu.__op){
+        case 0x65: // Zero Page
+          cpu.__mem.address = cpu.__opv;
+          cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+          cpu.__op = -1; break;
+        case 0x75: // Zero Page, X
+          cpu.__opv = (cpu.__opv + cpu.__XR) & 0xFF; break;
+        case 0x6D: // Absolute
+        case 0x7D: // Absolute, X
+        case 0x79: // Absolute, Y
+          cpu.__mem.address = cpu.__PC;
+          PCUp(cpu, 1);
+          cpu.__opv |= cpu.__mem.byte << 8; break;
+        case 0x61: // Indirect, X
+          cpu.__opv = (cpu.__opv + cpu.__XR) & 0xFF; break;
+        case 0x71: // Indirect, Y
+          cpu.__mem.address = cpu.__opv;
+          cpu.__opv = cpu.__mem.byte;
+          break;
+      }
+      break;
+    case 2:
+      switch (cpu.__op){
+        case 0x75: // Zero Page, X
+        case 0x6D: // Absolute
+          cpu.__mem.address = cpu.__opv;
+          cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+          cpu.__op = -1; break; 
+        case 0x7D: // Absolute, X
+        case 0x79: // Absolute, Y
+          let s = (cpu.__op === 0x7D) ? cpu.__XR : cpu.__YR;
+          let l = (cpu.__opv & 0xFF) + s;
+          cpu.__opv = (cpu.__opv & 0xFF00) | (l & 0xFF);
+          if (l < 255){
+            cpu.__mem.address = cpu.__opv;
+            cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+            cpu.__op = -1;
+          }
+          break;
+        case 0x61: // Indirect, X
+          cpu.__mem.address = cpu.__opv;
+          cpu.__opv = cpu.__mem.byte;
+          break;
+        case 0x71: // Indirect, Y
+          cpu.__mem.address += 1;
+          cpu.__opv |= cpu.__mem.byte << 8;
+          break;
+      }
+      break;
+    case 3:
+      switch (cpu.__op){
+        case 0x7D: // Absolute, X
+        case 0x79: // Absolute, Y
+          let h = (cpu.__opv >> 8) + 1;
+          cpu.__mem.address = (cpu.__opv & 0xFF) | (h << 8);
+          cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+          cpu.__op = -1; break;
+        case 0x61: // Indirect, X
+          cpu.__mem.address += 1;
+          cpu.__opv |= cpu.__mem.byte << 8;
+          break;
+        case 0x71: // Indirect, Y
+          let l = (cpu.__opv & 0xFF) + cpu.__YR;
+          cpu.__opv = (cpu.__opv & 0xFF00) | (l & 0xFF);
+          if (l <= 255){
+            cpu.__mem.address = cpu.__opv;
+            cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+            cpu.__op = -1; break;
+          }
+      }
+      break;
+    case 4:
+      if (cpu.__op === 0x71){
+        let h = (cpu.__opv >> 8) + 1;
+        cpu.__opv = (cpu.__opv & 0x00FF) | (h << 8);
+      }
+      cpu.__mem.address = cpu.__opv;
+      cpu.__AR = ALU(cpu, 0, cpu.__AR, cpu.__mem.byte);
+      cpu.__op = -1; break;
+  }
+  cpu.__step += 1;
 }
 
 function AND(cpu){
       break;
   }
 
-  cpu.N = BIT.isOn(t, 7);
+  cpu.N = (t >= 0x80);
   cpu.Z = (t === 0);
   cpu.__op = -1;
 }
   }
 }
 
+function MemAddrFrom(cpu, addr){
+  cpu.__mem.address = addr;
+  let v = cpu.__mem.byte;
+  cpu.__mem.address = (addr + 1) & 0xFF;
+  v |= cpu.__mem.byte << 8;
+  return v;
+}
+
+function ALU(cpu, m, a, b){
+  let v = 0;
+  switch(m){
+    case 0: // Addition
+      v = (a + b) + ((cpu.C === 1) ? 1 : 0);
+      cpu.C = (v >= 256);
+      break;
+    case 1: // Subtraction
+      v = (a - b) - ((cpu.C === 0) ? 1 : 0);
+      cpu.C = (v >= 0);
+      break;
+  }
+  v &= 0xFF;
+  cpu.V = (BIT.isOn(a, 7) === BIT.isOn(b, 7)) && (BIT.val(v, 7) !== BIT.val(a, 7));
+  cpu.N = BIT.val(v, 7);
+  cpu.Z = (v === 0);
+  return v;
+}
+
 // --------------------------------------------------------------------------------------------
 // --------------------------------------------------------------------------------------------
 // --------------------------------------------------------------------------------------------
     // Registers
     this.__PC = 0;   // Program Counter (16 bit)
     this.__SP = 255; // Stack Pointer (8 bit)
-    this.__PR = 0;   // Status Register (8 bit)
+    this.__PR = 32;   // Status Register (8 bit, bit 5 is always 1)
     this.__XR = 0;   // X Register (8 bit)
     this.__YR = 0;   // Y Register (8 bit)
     this.__AR = 0;   // Accumulator Register (8 bit)