instruction logic reference?

[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.

[BigDumbDinosaur]

JimDrew wrote:

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.

[Hobbit1972]

The SO pin:

Thowllly wrote:

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.

[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 

[BigEd]

Quite right. I wonder if they were experimenting using a buggy emulator.
Here's the proof:
http://visual6502.org/JSSim/expert.html ... a9ee0aeaea