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DirectPage and DirectPageIndirect

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This commit is contained in:
scawful
2023-08-19 20:12:56 -04:00
parent 7dcbc7f83c
commit 536136d8c9
5 changed files with 49 additions and 67 deletions
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24
src/app/emu/cpu.h
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@@ -75,7 +75,7 @@ class CPU : public Memory {
// JMP (addr, X)
uint16_t AbsoluteIndexedIndirect() {
uint16_t address = FetchWord() + X;
return memory.ReadWord(address);
return memory.ReadWord(address & 0xFFFF); // Consider PBR if needed
}
// Effective Address:
@@ -136,7 +136,10 @@ class CPU : public Memory {
// High/low: Direct Page Register plus operand byte
//
// LDA dp
uint16_t DirectPage() { return FetchByte(); }
uint16_t DirectPage() {
uint8_t dp = FetchByte();
return D + dp;
}
// Effective Address:
// Bank: Zero
@@ -168,7 +171,9 @@ class CPU : public Memory {
// LDA (dp, X)
uint16_t DirectPageIndexedIndirectX() {
uint8_t dp = FetchByte();
return memory.ReadWord((dp + X) & 0xFF);
uint16_t effective_address = D + dp + X;
uint16_t indirect_address = memory.ReadWord(effective_address & 0xFFFF);
return indirect_address;
}
// Effective Address:
@@ -180,7 +185,9 @@ class CPU : public Memory {
// LDA (dp)
uint16_t DirectPageIndirect() {
uint8_t dp = FetchByte();
return memory.ReadWord(dp);
// Add the Direct Page register to the fetched operand
uint16_t effective_address = D + dp;
return memory.ReadWord(effective_address);
}
// Effective Address:
@@ -191,7 +198,8 @@ class CPU : public Memory {
// LDA [dp]
uint16_t DirectPageIndirectLong() {
uint8_t dp = FetchByte();
return memory.ReadWordLong(dp);
uint16_t effective_address = D + dp;
return memory.ReadWordLong(effective_address);
}
// Effective Address:
@@ -204,7 +212,8 @@ class CPU : public Memory {
// LDA (dp), Y
uint16_t DirectPageIndirectIndexedY() {
uint8_t dp = FetchByte();
return memory.ReadWord(dp) + Y;
uint16_t effective_address = D + dp;
return memory.ReadWord(effective_address) + Y;
}
// Effective Address:
@@ -218,7 +227,8 @@ class CPU : public Memory {
// LDA (dp), Y
uint16_t DirectPageIndirectLongIndexedY() {
uint8_t dp = FetchByte();
return memory.ReadWordLong(dp) + Y;
uint16_t effective_address = D + dp;
return memory.ReadWordLong(effective_address) + Y;
}
// 8-bit data: Data Operand Byte