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This commit is contained in:
Irmen de Jong 2019-10-07 22:10:22 +02:00
parent f152443475
commit 9e15946f84
1 changed files with 4 additions and 4 deletions
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8
src/main/kotlin/razorvine/ksim65/Cpu6502.kt
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@ -761,12 +761,12 @@ open class Cpu6502 : BusComponent() {
fetchedAddress = regY + (lo or (hi shl 8)) and 0xffff
}
AddrMode.Ind -> {
// not able to fetch an address which crosses the page boundary (6502, fixed in 65C02)
var lo = readPc()
var hi = readPc()
fetchedAddress = lo or (hi shl 8)
if (lo == 0xff) {
// emulate bug
// emulate 6502 bug (fixed in 65C02):
// not able to fetch an address which crosses the page boundary.
lo = read(fetchedAddress)
hi = read(fetchedAddress and 0xff00)
} else {
@ -777,14 +777,14 @@ open class Cpu6502 : BusComponent() {
fetchedAddress = lo or (hi shl 8)
}
AddrMode.IzX -> {
// note: not able to fetch an adress which crosses the page boundary
// note: not able to fetch an address which crosses the page boundary
fetchedAddress = readPc()
val lo = read((fetchedAddress + regX) and 0xff)
val hi = read((fetchedAddress + regX + 1) and 0xff)
fetchedAddress = lo or (hi shl 8)
}
AddrMode.IzY -> {
// note: not able to fetch an adress which crosses the page boundary
// note: not able to fetch an address which crosses the page boundary
fetchedAddress = readPc()
val lo = read(fetchedAddress)
val hi = read((fetchedAddress + 1) and 0xff)