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Olduino/X – Kicking the AVR Habit

January 30, 2018

18-01-30 OlduinoX Fullsize Schematic.
Right from the beginning the 1802 Olduino has had an AVR co-processor that communicated with the host for loading and serial comm and generated the clock pulses for the hardware SPI shift registers.

With the narrow ROM and non-volatile RAM I can put the bootloader and bitbang serial into the 1802 and, with a few gates I can generate the SPI clock as well so the AVR is gone gone gone!
18-01-30 SPI CLOCK
I got the SPI clock circuit from Josh Bensadon on the 1802 list who also did the fast serial routines. The narrow ROM came from Herb Johnson also on the Cosmac list. Thanks guys!
IMG_0744
The first implementation is ugly with the 7390 decade counter and three input nor gate linked on a breadboard but i’m imagining they’ll fit pretty easily in the area where the AVR footprint and the icsp header are.

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