torsdag 15 januari 2009

The defunct CEGMON story

The original monitor-chip MONUK01 (yesterdays "BIOS" to some extent) was standard in the beginning and included in the kit that I assembled.
Soon I replaced it with the "New Monitor" that had some extra features, but also a lot of changes such as vectors and.... the flashing prompt that blurred the screen! Yes, I know it could be switched off by a POKE.

Later, when then I did the extended video mod, a new monitor was needed to support 32 lines.
I bought the CEGMON monitor (extended), a full featured monitor with a lot of good functionality, good documentation for 32 lines! I liked it a lot!
Unforturnately I zapped CEGMON EPROM in -84 when I did a printout of the EPROM content and swapped it with power ON! No supplier/agents were still in business in that time and I had no means of reprogramming a EPROM myself. This was the end!!...or..??
The disassembled printout w
ould later prove to be very important!
The CEGMON issue was resolved in Oct. 2008 by some help from the community.
From the printed listing I painstakingly started to type every byte into a freeware hexeditor (Neo), then sanity-checked the code in a freeware 6502 assembler (6502sim). Good tools by the way...
A helpful friend, found in a electronic forum after crying for HELP!, then programmed a 2716 EPROM for free. The 2716 and even the postage were w/o cost. Great! Thanks!

As you can see from the below picture, the UK101 booted up nicely with the new reborn CEGMON

Yes, it works! In full 32x48 !

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