bread80

@bread80@mstdn.social

Amstrad CPC, RC2014, Z80, Raspberry Pi Pico, TTL processors and the occasional bit of Eurorack

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bread80, 6 days ago to random

Now to get memory writes working in the Datapoint simulator. There's a /MEMORY_WRITE_READY input which needs to be driven. The circuit for this is on the keyboard decoder PCB.

Unconnected to the rest of that board, except for a POR output. Not the first bit of circuit I've found spilled onto a different board.

The circuit drives the /MEM_WRITE_READY line while the hardware bootloader reads data from tape. I can just glue it high for now.

#Datapoint #Datapoint2200

A close up of the power on reset and reboot circuit which drives the /MEMORY_WRITE_READY pin and others associated with bootloading.

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bread80, 6 days ago

For anyone who may not be aware, the Datapoint has no ROM (except character ROMs). At (re)boot times the machine rewinds the first tape deck and loads the first program record on it. This is done by directly driving the address counters in the processor.

And all of this is done in hardware.

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