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 Post subject: VIA 6522 vs W65C22
PostPosted: Mon Sep 16, 2024 4:25 pm 
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Joined: Sat Jan 09, 2021 9:33 pm
Posts: 24
Hello there,

On a vintage computer the ascii keyboard is connected to a parallel port.
Usually I have a real 6522 via for this port and this works very well.

I try to change the 6522 for a W65C22 and then start to see some strange things.
Some characters (as far I can see "g", "O", "o", "w", "?" and "7") sometime come in twice.
I double check the strobe signal and I am sure that there is only one down pulse per keystroke as expected...
If I read the datasheets (6522 and W65C22) I understand that the data on port is read one time when strobe go down and then is latched until the central processor read it. Only at this moment new data on port can be taken in account.

I must say that I am a little lost and cant understand how this is possible and why only some chars show the problem ???

Any help will be appreciated.
Thanks.
Philippe


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 Post subject: Re: VIA 6522 vs W65C22
PostPosted: Mon Sep 16, 2024 6:00 pm 
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Joined: Thu May 28, 2009 9:46 pm
Posts: 8503
Location: Midwestern USA
Do you have a schematic of the interface to the 6522 you can post?

Also, which version of the W65C22 do you have?  The version is signified by a part number suffix:

  • The W65C22N has an open-drain IRQ output and TTL-compatible inputs.  It is a drop-in replacement for the 6522.
     
  • The W65C22S has a totem-pole IRQ output and CMOS-compatible inputs.  It cannot directly replace a 6522 in a system using TTL (e.g., 74LS) logic and/or a wired-OR interrupt system.

If you have the W65C22S, obtain a W65C22N and give the latter a try.

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 Post subject: Re: VIA 6522 vs W65C22
PostPosted: Wed Sep 18, 2024 6:30 am 
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Joined: Sat Jan 09, 2021 9:33 pm
Posts: 24
I have a S version.

Asap I will give a try to a N version.

Regards.
Philippe


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