Re: PET 2001 RAM question

Years ago I used a couple of Jim Brain's adapters to replace a bad ROM and all the RAM on a 2001-8.

The ROM sockets are in parallel pairs, so you can remove one and replace the other one with a 2732.

With the addition of a few jumpers you can put a 27256 into the other ROM socket.

m

----- Original Message ----- 
From: "Ethan Dicks" <ethan.dicks@gmail.com>
To: <cbm-hackers@musoftware.de>
Sent: Thursday, February 01, 2018 2:14 PM
Subject: Re: PET 2001 RAM question


> On Thu, Feb 1, 2018 at 2:41 AM, Francesco Messineo
> <francesco.messineo@gmail.com> wrote:
>> On Thu, Feb 1, 2018 at 2:47 AM, Mia Magnusson <mia@plea.se> wrote:
>>> Den Tue, 30 Jan 2018 23:53:46 -0500 skrev Ethan Dicks
>>> <ethan.dicks@gmail.com>:
>>>> That's what I'm doing for my 2001-8.  I don't have enough working
>>>> 6550s to run an 8K machine, so I have a single 62256 on a CPU socket
>>>> board strapped for 8K.
>>>
>>> Did you remove all main RAms on the motherboard, or do you use some
>>> other method to make it not collide with the 62256?
>>
>> on a 2001 board, it would collide anyway because the 74LS244 on the
>> RAM data bus are enabled.
> 
> In case it's not clear, I was not implying I made my own board with
> only a 62256 on it.  I have several of these:
> 
> http://vic-20.de/x1541/hardware/petram.html
> 
>> On my PET RAM/ROM board (my own design as always) there's 74LS245
>> between the internal RAM/ROM, 6502 data bus and the external data bus
>> that's enabled only when the 6502 makes access to external addresses
>> (configurable).
> 
> Yes.  Nicholas Welte's design has a '245 for data bus buffering, and a
> GAL for deciding what accesses are onboard and which ones get passed
> through to the motherboard.  As I said, I don't have a ROM installed
> in mine because I happen to have a full working set of original 6540
> ROMs, but I can easily install multiple PET ROMs via a single 27256 if
> I decided to.
> 
> -ethan
> 
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