Apple II Plus 6502 vs. 6502a?

[tevion5]

I've noticed on the system requirement for a very cool looking Ethernet card for the Apple II, it says that it supports the Apple II plus but only if it has "6502a" or higher.

I understand the Plus has just a regular 6502 processor in it. Therefore was the 6502a an upgrade or expansion card for the II plus, or did later models come with a different processor or something?

Ref: http://a2retrosystems.com/support.htm#why

 

[tdiaz]

The 6502 is a 1MHz design, and the 6502A is designed for 2MHz, is also more prevalent.

.. and with that, the unique characteristics of the II design come into play.

As a programmer, if you are so anally relying on timing to accomplish stuff and your code does not run on something, it's probably because there's a 6502, not A, in there. Or the other way around.

Mostek produced the 6502A, and it was intended to be 100% compatible with the MOS 6502, though it's designed around a 2MHz clock. Think Apple ///.

From there on out, further 6502x derivatives were built on that.

 

[tyche]

I believe it's possible to put in 6502A in ][ or ][+ only some software that relies on specific timing would fail. There were accelerators for the pre-//e line that could go ~4MHz but had a fallback key on boot up to run at 1MHz to keep it compatible.

Maybe the card is compatible with ]['s with accelerator chips as well hence the > 2MHz mention.

 

[tdiaz]

Yes, putting a 6502A in the oldest II's isn't an issue. There are -far more- 6502A's out there, and any compatibility is going to be built on the highest percentage of the marketshare.

But the Uthernet specs are written because it's been established that it -does not- function without the 6502A.

 

[tevion5]

Yes, putting a 6502A in the oldest II's isn't an issue. There are -far more- 6502A's out there, and any compatibility is going to be built on the highest percentage of the marketshare.

But the Uthernet specs are written because it's been established that it -does not- function without the 6502A.

Ahh so a run of the mill II plus will not have the "a"?

 

[tdiaz]

Ahh so a run of the mill II plus will not have the "a"?

It's possible, I've seen them both ways. "Check first" and get one at the same time, if needed..