7800 uses an undocumented Sally pin.

[Bryan]

I noticed the 7800 schematics use pin 36 (and call it JK) of the 6502C. This is normally a NC pin on the 6502 and it isn't used in other Atari systems. Is there any data out there on what this pin does?

 

EDIT: Okay, it seems the 7800 schematics call pin 34 R/W which is normally a NC. It's pin 36 that it calls JK, which is normally called R/W. The 5200 schematic has them tied together too. The XL schematics only uses 36. On a real 6502, it's pin 34. Very confusing.

 

-Bry

Edited July 6, 2008 by Bryan

[+Omegamatrix]

I haven't looked at the schematic of the 6502 IC but Toggle popped into my head instead of No Change.

[SeaGtGruff]

I noticed the 7800 schematics use pin 36 (and call it JK) of the 6502C. This is normally a NC pin on the 6502 and it isn't used in other Atari systems. Is there any data out there on what this pin does?

 

EDIT: Okay, it seems the 7800 schematics call pin 34 R/W which is normally a NC. It's pin 36 that it calls JK, which is normally called R/W. The 5200 schematic has them tied together too. The XL schematics only uses 36. On a real 6502, it's pin 34. Very confusing.

 

-Bry

I'm not sure about pins 34 and 36, but one of them is "R/W," and the other is (I believe) unused-- I'm just not sure which is which. However, the notes I was making for myself indicate that pin 35 of the 6502C is used for "HALT," whereas pin 35 of a normal 6502 is "NC" (not connected, or unused).

 

Michael

[Bryan]

Well, I checked a real Sally/6502C/C014806 and pin 34 appears to not be connected. There's no output and it does not respond to being tied high or low, or shorted to any other pin. Strange that it's included in the schematic.