RE: (Fwd) 65816->6502

From: Baltissen, GJPAA (Ruud) <ruud.baltissen_at_apg.nl>
Date: Wed, 14 Mar 2018 07:35:13 +0000
Message-ID: <54F350D2C6501448A3EE14B7854C5FB57521DBA8@WSV10441N3.office01.internalcorp.net>
Halo allemaal,


Mia schreef:
> On PET (except 8096/8296), VIC-20 and 1541, it's as we all know not that nice. Therefore
> IMHO a 65816 add-on for those computers should preferable also contain ram and a
> mechanism to bank switch between that ram and the computers built in stuff.

IMHO it isn't that hard. I expanded a VIC-20 with an ISA interface so I could use an old RAM expansion card as extra memory. This card is equipped with 128 KB SRAMs so no problems with refresh. The interface was made in a quick and dirty way by piggybacking the ICs on top of the existing ones of the VIC-20. It worked more or less because I found out I made a mistake due to the lack of knowledge at that time: RDY did not work as I expected. Even if RDY is negated, the 65816 keeps on outputting address lines A16..23 on the data bus. I did find a solution for it at the end but didn't implement it here because of the work involved.

What is needed:
- a 573 for creating the address lines A16..23
- two 541s for generating the address bus towards the original system + pull-up resistors
- one 125 gate for the R/W line + pull-up resistor
- a 245 between the 65816 and the original system
- a 688 for detecting if bank 0  = original system is accessed
- four NAND gates = one 00 for handling RDY
- some glue logic

The idea is simple: as long as the 65816 accesses the original system, the 541s forward the address lines A0..15 towards it. Accessing any other bank will tri-state the address lines and R/W line. The resistors will make the original system think that address $FFFF needs to be read. Save enough IMHO. The 245 makes sure that the outputted data does not reach the 65816.
I'll see what is on schematic and I will upload it to my site.


Met vriendelijke groet / With kind regards, Ruud Baltissen

www.Baltissen.org




De informatie in dit e-mailbericht is vertrouwelijk en uitsluitend bestemd voor de 
geadresseerde. Wanneer u dit bericht per abuis ontvangt, verzoeken wij u contact op te 
nemen met de afzender per kerende e-mail. Verder verzoeken wij u in dat geval dit 
e-mailbericht te vernietigen en de inhoud ervan aan niemand openbaar te maken. 
Wij aanvaarden geen aansprakelijkheid voor onjuiste, onvolledige dan wel ontijdige 
overbrenging van de inhoud van een verzonden e-mailbericht, noch voor daarbij 
overgebrachte virussen.

APG Groep N.V. is gevestigd te Heerlen en is ingeschreven in het 
handelsregister van de Kamer van Koophandel Limburg onder nummer 14099617


The information contained in this e-mail is confidential and may be privileged. 
It may be read, copied and used only by the intended recipient. 
If you have received it in error, please contact the sender immediately by 
return e-mail; please delete in this case the e-mail and do not disclose its 
contents to any person. We don't accept liability for any errors, omissions, 
delays of receipt or viruses in the contents of this message which arise as a 
result of e-mail transmission.

APG Groep N.V. is registered in the trade register of the Chamber 
of Commerce Limburg, The Netherlands, registration number: 14099617

Received on 2018-03-14 22:44:20

Archive generated by hypermail 2.2.0.