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Re: instruction logic reference?
Posted: Thu Jun 25, 2015 10:35 pm
by JimDrew
There is an error in the information on this website concerning interrupts. Please see:
http://homepage.ntlworld.com/cyborgsyst ... 02.htm#INT
Look at the last line under the "How can I DISable Interrupts?" section:
# This is done with the STI instruction.
Looks like someone was thinking 80x86 when they wrote that.
Re: instruction logic reference?
Posted: Fri Jun 26, 2015 4:54 am
by BigDumbDinosaur
There is an error in the information on this website concerning interrupts. Please see:
http://homepage.ntlworld.com/cyborgsyst ... 02.htm#INT
Look at the last line under the "How can I DISable Interrupts?" section:
# This is done with the STI instruction.
Looks like someone was thinking 80x86 when they wrote that.
That page has a number of errors that have persisted for a number of years. Better to read Garth's interrupt primer, which is accurate.
Re:
Posted: Fri Jun 26, 2015 6:05 am
by Hobbit1972
The SO pin:
Input, the pin effect the register. I think it's edge sensitive, but don't remember which edge.
The falling edge of SO pin will set the oVerflow bit.
Re: instruction logic reference?
Posted: Tue Sep 29, 2015 6:51 am
by giszo
I was reading the instruction reference of ASL while I noticed that the example is incorrect.
The pseudocode of the logic is saying that the highest bit is shifted into the Carry flag (P.C = B.7), but the below example is setting Carry to zero, while the highest bit before the shift operation was one.
Code: Select all
Before:
P.C = ? B = 1 1 1 0 1 1 1 0
After:
P.C = 0 B = 1 1 0 1 1 1 0 0
Re: instruction logic reference?
Posted: Tue Sep 29, 2015 8:44 am
by BigEd
Quite right. I wonder if they were experimenting using a buggy emulator.
Here's the proof:
http://visual6502.org/JSSim/expert.html ... a9ee0aeaea