30 Dec
2002
30 Dec
'02
10:02 a.m.
On Mon, 30 Dec 2002 pete(a)dunnington.u-net.com wrote:
On Dec 28, 19:53, Sellam Ismail wrote:
Sorry, it was a typo. I meant two 8-bit ports.
The next step is to wire in the data signals and
start to read data. The
VIA gives me two 16-bit ports and an additional 4-bit port.
That's an odd VIA. You mean a single 6522, right? It has two
bidirectional 8-bit ports, each of which has 2 associated handshake lines.
Each of the bidirection lines can be set to be an input or an output, so
it might seem like you have 16 possible inputs and 16 possible outputs --
but you only have 16 connections (plus 4 handshake). should do it. Don't bother with interrupts to
start with. Leave the IER
all zeros, and just poll the IFR to look for the flag for CA1. Or just
poll it looking for a negative number (which means bit 7 is set, which
means one of the other flags is also set).
This is starting to make sense.
But alll the documenation I've read so far indicates that the function of
the CA and CB lines is controlled by the PCR (Peripheral Control
Register). I'll go poke a 0 into the IER and then see if I can get bits
in the IFR to toggle by putting +5 on the CA1, CA2, CB1 or CB2 pins.
Sellam Ismail Vintage Computer Festival
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