Re: 6809 assembly knowledge needed

From: Nate Lawson <>
Date: Thu, 04 Feb 2010 22:17:24 -0800
Message-ID: <>
Jim Brain wrote:
> On 2/4/2010 12:52 PM, Nate Lawson wrote:
>> Rainer Buchty wrote:
>>> On Wed, 3 Feb 2010, wrote:
>>>> - The PDF says: "I/Os are not 5V tolerant". I see a lot of resistors
>>>> to handle this. But is it still capable of driving the C64 plus some
>>>> extras? If not, what is needed to make it capable? For example, will
>>>> 74HCT245's and 541's do?
>>> You don't need extra level shifters as GODIL comes readily equipped with
>>> such. These you can use (adds 700ps to the timing path), but you don't
>>> need to in case you don't require 5V tolerance.
>> Right, and you can configure the board for either the level shifter or
>> series resistors.
> How do you do the selection?  I can see turning off the level shifters
> by deselecting the 16211 bus transceivers, but how do you turn on series
> resistors?  Are they just always populated in parallel with the bus
> drivers?
> I ask because I am working on a C64/128 expansion port (think CMD EX3 or
> FB-EX3, etc.).  I've been asked to put some bus drivers on the board to
> clean up the C64 bus.  SOme other designs are using '541s and 245s, but
> those have way too long of latency.  The 16211 looked interesting
> because it only has a tiny < 1ns latency, but I would prefer a way to
> deselect it if someone finds carts that do not like it.

See page 30 of this pdf:

           |     R18
PIN40------o----/\/\/-----o--F02 (on FPGA)
           |              |

R17 is populated, R18 is not. According to page 16, you have to solder
bypass resistors (R18 in this case).

It is not software-configurable. You have to decide on direct IO with
pullups or level shifter at assembly time. I suppose you could provide
jumpers or DIP switches also.


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Received on 2010-02-05 07:00:03

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