Re: ROM Dump of Amiga Keyboard controller

From: Jim Brain <>
Date: Sun, 29 Jun 2014 12:00:26 -0500
Message-ID: <>
On 6/29/2014 4:15 AM, Gerrit Heitsch wrote:
> 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.
>  Gerrit
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Sorry, I should clarify:

Still working out how to create.... using parts from my spare parts bin 
:-)  10.6 zeners are not in my bin right at present.  It's OK, I took a 
12V and dropped it through 3 PN junctions, so I think I'll have 9.9V...  
a diode and 10K feeds 5V to RESET, and two 2n3904s either dump 10V to 
the pin or drive it to ground.

I'm cobbling together some code right now.


Jim Brain

       Message was sent through the cbm-hackers mailing list
Received on 2014-06-29 18:00:02

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