Re: ROM Dump of Amiga Keyboard controller

From: Jim Brain <>
Date: Sat, 28 Jun 2014 23:53:16 -0500
Message-ID: <>
On 6/28/2014 12:12 PM, Gerrit Heitsch wrote:
> On 06/27/2014 02:15 AM, Kajtár Zsolt wrote:
>> Hash: SHA1
>>> As before, I still don't have a clear picture of how exactly is this
>>> supposed to work. Either this or the (presumably simpler) approach with
>>> an EPROM and a 4040. I think I am not alone in this and that is one of
>>> the reasons nobody (including myself) haven't done it yet.
>> It works the same way as the EPROW+counter approach. Except that the 
>> external
>> 6502 is the "counter" for addressing the EPROM. Which has the benefit of
>> inserting dummy fetches automatically to the bus when needed. This 
>> way you
>> could use any assembler/monitor to produce the code for the EPROM, 
>> without
>> tricks. And this 6502 could be used for the communication with the 
>> 6500/1 to
>> dump it's content too.
> An idea worth thinking about. You still have that clock divided by 2 
> problem though and have to make sure somehow that the two 6502 are not 
> off by half a cycle.
>  Gerrit
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I have sitting on the bench, a 6500/1 I pulled from a 1520 here, and a 
ATMEGA644P.  Not sure I have a 20MHz crystal, but i have a 16MHz one.  I 
am happy to whip up some code to try here, but any help would be 

I'll set up a 250kHz square wave on one of the OC outputs.  global var 
will track first or second cycle.

one pin will set RESET to 10V or 5V.  Still working out how to create 
the voltage difference at the RESET pin.  I can tie RESET  to 5V through 
a IO pin and a diode, and then put a transistor on 10V PSU output, but 
then that will be 9.3V.  I am not sure I have a 10.7V PSU output.

PORTC will be tied to a port on the AVR

PORTB will be tied to a different port.

What I'd like help with is a sequence of bytes (including any dummy 
bytes needed) to sending to portC once I release RESET and drive it to 
10V.  At first, I'd like to start with something that will accomplish 
something on portb as quickly/simply as possible, like driving all pins 
to 1 or 0 or something.  I figured maybe I could tweak things until it 
works, and then I might be able to do something more complex.


Jim Brain

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Received on 2014-06-29 08:00:03

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