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Old 1st Jan 2018, 4:22 pm   #12
RogerEvans
Hexode
 
Join Date: Oct 2014
Location: Wiltshire, UK.
Posts: 378
Default Re: 8085 processor questions

There are a couple of display controllers from this period that i am familiar with. More common was the Motorola 6845 which generated all the clock signals for character generation and sync pulses and had a separate character generator memory which could be ROM or RAM, RAM offered you user definable characters. The 6845 will only generate proper sync pulses after its registers have been initialised so if you have a 6845 and a stable picture then the CPU is doing at least some of its initialisation.

Less common and very down market was the 6847 which would generate NTSC signals including the colour burst. It was low resolution and I doubt you would find it in a serious instrument (it was used in some of the home computers like the Dragon 32). The 6847 generates all the timing and colour signals without any external initialisation.

I am sure there must have been other packaged display controllers and it was not uncommon to do all the timing signals in 74LS logic, probably a dozen chips.

If you could post a list of all the large chips (more than 20 pin) it might help to guess what is what.

Roger
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