Re: C64 Kernal disassembly question

From: Jim Brain (
Date: 2004-05-13 06:53:18

OK, so looking at the serial port, and the timing information on it, 
here's a question:

I see 4 pins in the IEC port of interest to a protocol:

SRQ (only on burst devices)

Reset is marginally important for my purposes.

I'm implementing a controller to handle IEC traffic and convert to 
serial or other.  In know C2N232 and Krokos' code do it, and I'll borrow 
from that source.

But, since I may have RS232 ints coming into the controller, I'd rather 
not do a straight timed bit bang implementation of the protocol.

I have a few interruptsI want to do other things while I am transferring 
data to the 64.  Since I have an AVR controller, I have 4 external 
interrupt pins I can use to monitor these lines.

The question is how many pins should I monitor via an interrupt?

In the normal protocol, CLK needs one, SRQ isn't used, ATN has one in a 
15X1, but doesn;t look like it needs it (just check ATN when you start 
clocking the byte in), and DATA only seems to need one if you are the 
TALKER (checking for DATA hi after setting CLK hi for the preamble, 
checking for low at end)  So, CLK/DATA for normal protocol

Burst seems to need SRQ/DATA/CLK as well.

I know some speeders use ATN to clock data, so I assume ATN/CLK/DATA as 
an option

JDOs uses a timed approach, which I can handle via a timer inside the CPU.

Are there any ATN/SRQ/DATA/CLK type protocols out there?  If not, it 
looks like I could just use 3 IRQ lines...


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