6502/py65
1
0
Fork 0
mirror of https://github.com/mnaberez/py65.git synced 2024-07-03 05:29:27 +00:00
Code Issues Projects Releases Wiki Activity

rewrite ADC decimal mode - now passes the sole test

Browse Source
This commit is contained in:
Ed Spittles 2010-12-13 13:14:30 +00:00
parent b234ac4c32
commit 93d07b88ba
1 changed files with 25 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
src/py65/devices/mpu6502.py
View File

@ -281,21 +281,33 @@ class MPU:
data = self.ByteAt(x())
if self.p & self.DECIMAL:
if self.p & self.CARRY:
tmp = 1
else:
tmp = 0
data = convert_to_bin(data) + convert_to_bin(self.a) + tmp
halfcarry = 0
decimalcarry = 0
adjust0 = 0
adjust1 = 0
nibble0 = (data & 0xf) + (self.a & 0xf) + (self.p & self.CARRY)
if nibble0 > 9:
adjust0 = 6
halfcarry = 1
nibble1 = ((data >> 4) & 0xf) + ((self.a >> 4) & 0xf) + halfcarry
if nibble1 > 9:
adjust1 = 6
decimalcarry = 1 # may be a little more complicated than this
# the ALU outputs are not decimally adjusted
aluresult = (nibble1 << 4) + nibble0
# the final A contents will be decimally adjusted
nibble0 = (nibble0 + adjust0) & 0xf
nibble1 = (nibble1 + adjust1) & 0xf
self.p &= ~(self.CARRY+self.OVERFLOW+self.NEGATIVE+self.ZERO)
if data > 99:
self.p |= self.CARRY + self.OVERFLOW
data -= 100
if data == 0:
if aluresult == 0:
self.p |= self.ZERO
else:
self.p |= data & 128
self.a = convert_to_bcd(data)
self.p |= aluresult & self.NEGATIVE
if decimalcarry == 1:
self.p |= self.CARRY
if ( ~(self.a ^ data) & (self.a ^ aluresult) ) & 0x80:
self.p |= self.OVERFLOW
self.a = (nibble1 << 4) + nibble0
else:
if self.p & self.CARRY:
tmp = 1
@ -312,7 +324,7 @@ class MPU:
if data == 0:
self.p |= self.ZERO
else:
self.p |= data & 128
self.p |= data & self.NEGATIVE
self.a = data
def opROR(self, x):