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SPI Clock Without the AVR

January 21, 2018

18-01-21 SPI Clock

This is my attempt to generate the 8 pulses I need for the SPI clock without using the AVR.  CLOCKis the CPU clock, OUT2 is a positive going pulse generated when N1 goes high and /MRD is low.  I got this from Josh Bensadon but i’m not sure I’ve got it right.

UPDATE: After talking to Josh I’m still not completely sure about this but i do know i need a shoter positive going pulse for OUT2.  Fortunately the pulse that loads the shift register is at the right time although negative going.  I only want to do this when i’m doing output but i have an unused nor gate in the 7427 so the schematic below should be closer to correct.  I have the 7427 and 74390 on their way from digikey so i should be able to mock this up tomorrow. The second image shows the CPU pulses during an OUT 6 operation.  The OUT2TPB signal is labelled S1 in the hand drawn picture to correspond to josh’s schematic at bottom.

18-01-23 SPI Clock


18-01-23 josh's clock

Assuming all of this worked I would have the basis for a new version of the olduino that would leave out the AVR completely and possibly have SPI at two or three times the speed. Call it 1802 OlduinoX.



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