[chbot] Vintage computers show and tell...
zl3ag at radioengineering.com
Tue Sep 27 13:03:10 BST 2016
That deserves an article written for theregister.co.uk !
On 28/09/2016, at 12:39 AM, Richard Jones wrote:
> Somewhere in the garage I have a circa 1978/79 verowire Visual Display pcb that I developed for Acorn Computers that was the marriage of the Motorola MC6845 CRTC and the Mullard SAA5050 Teletext character generator IC. Chris Turner and Roger Wilson at Acorn asked me to develop an 80 character per line monochrome display for their Eurocard computer range and I offered to design them colour teletext display instead, which they accepted. Hermann Houser agreed to pay me with a 6502 CPU, and 8k RAM memory boards. The 6845 and SAA5050 combination became the heart of their BBC computer offering which won the BBC contract, possibly because of the assumed compatibility with over the air teletext. I used alternate half cycles of the 6809/6502 phi2 clock to allow the CPU transparent access to the memory mapped display ram while the character generator used the alternate half cycle for display access. Heady stuff for its day, given that at work I was using a teletype to print software listings and a hex keypad to enter programs in hand coded machine code for the National Semiconductor SC/MP.
> I'll see if I can find the board and bring it along to the next meeting.
> Richard Jones
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