65c22

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Vyper68
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65c22

Post by Vyper68 » Sun May 26, 2019 10:24 am

Hi
Has anyone got any experience of fitting a 65c22 in place of the normal 6522A in a Oric-1 or Atmos? I read a bit about the pull-up resistor needing to be removed on the IRQ line but it's part of a Resistor Network so would you cut the track?
Also there is talk of a diode being fitted but does not specify where this would be fitted.
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Re: 65c22

Post by mikeb » Sun May 26, 2019 4:48 pm

The pull up resistor also connects to the 6502 IRQ input, and any external peripherals. Removing it may well have unintended effects.

What is the source of this knowledge that the resistor should be removed?

The only other thing to check is the physical order/routing of the track, you may find that cutting the track to the SIL/DIL resistor pack also disconnects the 6502/6522/expansion port pin, depending on the exact direction the track takes, so you may need to cut in TWO places (either side of the resistor pin) and then remake a link between them. Check the board carefully!

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Re: 65c22

Post by Vyper68 » Sun May 26, 2019 5:37 pm

Here is the link to the info I found on the 65c22

http://wiki.defence-force.org/doku.php? ... :via_65c22
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Re: 65c22

Post by Chema » Sun May 26, 2019 7:01 pm

I'm sorry I completely suck at electronics, but a quick search gave this
There is a major design difference between the W65C22S and all previous versions of the 6522 and 65C22. The IRQB pin on the W65C22S is a standard totem pole output. It is no longer open drain and cannot be wire OR'ed.
And also some discussion about this here http://forum.6502.org/viewtopic.php?p=895

It seems that the IRQ line cannot be used in the same way as in a 6522 (no wire-OR) and, even with the modifications suggested in the wiki, you won't be able to use some important devices, such as a disk controller...

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Re: 65c22

Post by Vyper68 » Mon May 27, 2019 8:13 am

Thanks Chema, the one I have coming is a Rockwell part R65c22 not the newer WDC version so I might have more success with it.
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Re: 65c22

Post by iss » Mon May 27, 2019 8:36 am

Here is the proper place for the 'magic' IRQ diode:
65c22-IRQ-diode.png
But still compatibility issue can be expected.

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Re: 65c22

Post by Vyper68 » Mon May 27, 2019 2:20 pm

Thanks iss that is very helpful, when it arrives I will fit this and report back on how well it performs compared to my 6522A in my Atmos. :D
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Re: 65c22

Post by mikeb » Mon May 27, 2019 5:22 pm

I see, thanks for the link/context

The above diode suggestion by @iss will solve the problem (make sure it's in line with only the 65C22 leg, as per my caution on physical layout issues) -- the 65C22 having "totem pole" output means it will try and drive the line both HIGH (when idle) and LOW (when interrupting).

This is at odds with the 6522, which lets it float (when idle) and drives low (when interrupting). Hence the pull up resistor to allow float to be a "high" that someone else can override.

This means that multiple devices can assert the line (low) without treading on each other.

Removing the resistor would NOT help in Oric's specific case -- granted the 65C22 will drive the 6502 just fine, but you would have to forego ever using the external IRQ line on the expansion port, making it an incompatible Oric. Worse, if an external chip tries to drive the line low, and the internal 65C22 is driving high, you have an argument there. The sort resolved by small smoke signals from things, probably whichever chip was most expensive.

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Re: 65c22

Post by retroric » Tue May 28, 2019 12:25 am

Hi,

That's an interesting discussion, but I think an important point was omitted:

What is the intended purpose of replacing the stock 6522 with the CMOS 65C22 version?

I guess the CMOS version probably corrects bugs in the original NMOS units, but I don't remember these bugs affecting our Orics in any way (contrary to the C64 1541 disk controller for instance, where the 6522 serial shift register bug meant some disk routines using hardware shifts had to be completely rewritten in software, hence the very poor throughput of the disk unit).
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Re: 65c22

Post by Vyper68 » Tue May 28, 2019 8:02 am

retroric wrote:
Tue May 28, 2019 12:25 am
Hi,

That's an interesting discussion, but I think an important point was omitted:

What is the intended purpose of replacing the stock 6522 with the CMOS 65C22 version?

I guess the CMOS version probably corrects bugs in the original NMOS units, but I don't remember these bugs affecting our Orics in any way (contrary to the C64 1541 disk controller for instance, where the 6522 serial shift register bug meant some disk routines using hardware shifts had to be completely rewritten in software, hence the very poor throughput of the disk unit).
My main reason was curiosity as I have a 65c02P4 in my rebuilt Oric-1 and was interested to see if the same could be applied to the 6522A and fit a 65c22 in it. The info on the Wiki indicated that it was possible with some adaptation and it was interesting to see if anyone had else had tried and succeeded or failed, interesting either way.
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Re: 65c22

Post by Dbug » Tue May 28, 2019 2:52 pm

retroric wrote:
Tue May 28, 2019 12:25 am
where the 6522 serial shift register bug meant some disk routines using hardware shifts had to be completely rewritten in software, hence the very poor throughput of the disk unit).
The shift register feature does not work on all the Orics.

Twilighted used that for some of his sound routines, and in on of our demos there's a scroller at the end appearing on some tv snow effect, it's supposed to have some sample sound playing, it does not work on half of the machines I tried it on.

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Re: 65c22

Post by Steve M » Thu May 30, 2019 5:10 pm

I sold a couple of Oric boards to a guy that reckoned the 65c22 wasn't compatible with the Oric. He said 65c02 was fine but not the 65c22. I'm not sure what the difference is that make it a problem, but I've tried to stick to 6522 as long as I can.

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Re: 65c22

Post by Vyper68 » Thu May 30, 2019 6:42 pm

I have ordered some more 6522A’s so hopefully I will get the correct ones this time, last time they sent 6522P’s. The 65c22 was just an interesting idea to think about.
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Re: 65c22

Post by Silicebit. » Sat Jun 01, 2019 8:01 pm

The W65C22N is designed to be compatible with 6522, you must order the W65C22N not W65C22S.

From The Western Design Center:

W65C22S/W65C22N Differences
  • The W65C22S is lower power, faster and direct drive outputs with no current limiting resistors on outputs ports.
  • The W65C22N is plug replacement of NMOS 6522 devices with current limiting resistors on output ports.
  • The W65C22N does not have bus holding devices on the input, IO pins.
  • The W65C22N IRQB is an open drain output that CAN be Wire-ORd, unlike the totem-pole output of the W65C22S (some customers have had to use a diode in series with the IRQB output when using the W65C22S in their systems that had Wire-ORd interrupts).
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Re: 65c22

Post by Vyper68 » Sun Jun 02, 2019 11:28 am

Silicebit. wrote:
Sat Jun 01, 2019 8:01 pm
The W65C22N is designed to be compatible with 6522, you must order the W65C22N not W65C22S.

From The Western Design Center:

W65C22S/W65C22N Differences
  • The W65C22S is lower power, faster and direct drive outputs with no current limiting resistors on outputs ports.
  • The W65C22N is plug replacement of NMOS 6522 devices with current limiting resistors on output ports.
  • The W65C22N does not have bus holding devices on the input, IO pins.
  • The W65C22N IRQB is an open drain output that CAN be Wire-ORd, unlike the totem-pole output of the W65C22S (some customers have had to use a diode in series with the IRQB output when using the W65C22S in their systems that had Wire-ORd interrupts).
Thanks for the information, however, I have ordered the older Rockwell version ( R65C22P4 ) which I think falls into the same category as the W65C22S. We will see when it arrives.
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