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Old 25th Feb 2024, 11:56 am   #111
coolsnaz2
Tetrode
 
Join Date: Aug 2020
Location: Wallington, Greater London, UK.
Posts: 88
Default Re: Tiny SC/MP system !!!

I have modified a Tiny SC/MP board to accept NVSRAM (DS1245Y) in place of the RAM/ROM chips and the GAL16V8 has been replaced with the GAL22V10 version.

2 fly leads are required to give the MK14 access to 54k of NVSRAM. My current configuration in the GAL gives me 4k ROM and 50k RAM.
The GAL is being used to decode A12-A15 lines from D0-D3 using the NADS pin on the SCMP.

The 2 fly leads are used to select only page zero for the Keyboard/Display D00, and the I/O chip at 800. The shadow memory locations for the Keyboard/Display and the I/O chip have been maintained on page zero.

Slight modification are required to the MK14 board, two IC’s require a pin to be removed from their socket and the appropriate fly lead inserted into the socket. Issue V and VI MK14 replicas require slightly different locations for the fly leads to be connected.

Currently my VDU card cannot select just page zero, so the VDU memory at 0200-03FF is shadowed across all pages. Unfortunately this restricts the amount of continuous memory to 3k on any one page. This limitation may be fixable in the future.

Next step is to create a new PCB for the modified board.
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