Re: User Port and AutoRun Addresses

From: Nate Dannenberg (natedac_at_kscable.com)
Date: 2001-02-02 18:13:06

> >> What is the pinout of the userport regarding datalines only, is it C64/V20 compatible?
> >
> >RS232 is operated via a 6551 (aka swiftlink) chip in the plus 4, and 
> This must be only for the lines related to the RS-232 which are software controlled on the C64... so modems are compatible, but I'm specifically interested in where the lines for the 6529 come out for an 8-bit interface
> 
> Now that I remember my other, what is the bit assignment for the IEC
> lines? I recall that they got to the on-CPU I/O port.

On the C128, 'slow' serial is handled by the same lines as on the C64,
$DD00 bits 7-3 (ATN, clock out, data out, clock in, data in, in that
order).

'Burst' Serial is handled by a hardware serial shift-register,
specifically $DC0C, CIA #1 Serial Port, along with the 'CNT' (hardware
clock) line associated with it.  These are CNT1 (pin 4) and SP1 (pin 5) on
the user port, which I didn't list earlier.

I forget if 'Fast' Serial mode is handled by software or by hardware
assist.

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