Re: ROM Dump of Amiga Keyboard controller

From: Gerrit Heitsch <>
Date: Sun, 29 Jun 2014 11:15:32 +0200
Message-ID: <>
On 06/29/2014 06:53 AM, Jim Brain wrote:
> 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.

How about something like they used on the tape port of the C64 or C16?

A transistor with a 10.6V zener diode between base and GND plus a pullup 
resistor between base and collector with the collector hooked up to the 
PSU (which should supply about 14V). The emitter is connected to the 
_RESET pin plus maybe a resistor to GND to allow for some current flow. 
That takes care of the 10V. Now put another zener (around 5V, might need 
some experimenting to find the correct value) parallel to the first one, 
but only route it to GND via a gate from a 7406 and maybe another gate 
from the same 7406 to pull the base of the transistor to GND to allow 
for a reset.

This way you need 2 portbits. One to switch between 10V and 5V and the 
other allow for a LOW on the RESET pin no matter what the other one is 
set to.


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Received on 2014-06-29 10:00:03

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