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6522 vs W65C22

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Wawavoun:
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 by 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

Alex Eisenhut:
You need to read the caveats section of the WDC datasheet.
"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. "

Which computer is this?

Wawavoun:
Of course I read it.

IRQ is not involved in the problem.

Ascii data come in to port A bits 0-6 and strobe is connected to CA1.

Data are read by polling.

The computer is a rebuild from the Elektor EC-6809.

Alex Eisenhut:
I understand that but I can't find a schematic. How are you displaying this data? Terminal?
It doesn't matter if the 6522 is polled, if it's pulling the IRQ line high, other things connected to the IRQ line may have problems signalling correctly, like a UART...

Also there's more than one W65C22 ...
https://www.westerndesigncenter.com/wdc/w65c22-chip.php

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).

Wawavoun:
I have a S version.
Its look to me that the N version is better in case of replacement of original 6522.

In fact the A port and the strobe signal of the via are directly drive by a Arduino Nano acting as a ps2 keyboard to parallel ascii converter.

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