Subj : Re: User Port Pins
To   : cbmeeks
From : Pekka Takala
Date : Thu Sep 27 2018 06:56 pm

On 25.09.2018 20:42, cbmeeks wrote:
> I'm curious about how to access certain pins of the C64 User Port.  Going by 
the pinout here:
>
> https://www.c64-wiki.com/wiki/User_Port
>
> I see there are some pins I'm not familiar with.
>
>
> 4       CNT1	Counter 1, from CIA #1
> 5	SP1	Serial Port 1, from CIA #1
> 6	CNT2	Counter 2, from CIA #2
> 7	SP2	Serial port 2, from CIA #2
These come from appropriate pins from appropriate CIA chips. You can use
these for fast serial connections. The clock comes from cnt pin and data
from sp1. Or if you input something, the chip reads from sp1 when clock
signal comes.

> 8	/PC2	Handshaking line, from CIA #2

I do not exactly know about this.

> 9	ATN	Serial attention in

I do not know why this is here. It is the same signal as in serial port.
Could it be that CBM thought that serial ports could be used with fast
drives?

> ...
> B	/FLAG2	Flag 2

A handshake line. This can be tied to a interrupt.
> ...
> M	PA2	PA2

You can use this pin as PB0-7. It has a DDR register and you can use it
as input or output. Usually used as handshake line.
>
>
> I have a basic idea what the counters are for but I'm looking for more 
detailed information on all of those pins.
>
> Are there any programming and/or schematics out there that indicate how to 
use them in various projects?
>
> Thanks
>
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