Uploaded August 2022 | Updated September 2026, 3 weeks ago

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SYN600 upgrade to CEGMON ROM
EEPROM 2816 Monitor ROM replacement
Pin 20 (assigned to the non-inverted phi-2 clock) is now connected to GND
Pin 21 is connected to +5V to ensure no writes to a 2816 EEPROM can occur.
Pin 18 is now connected to U18 – pin 4) /MCS signal which is active-low.

Sources:
Dave's OSI page osiweb.org
Professor Mark Csele Series 600 (Challenger 1P / Superboard) page technology.niagarac.on.ca/people/mcsele/hobby/ohio-scientific-computers-series-600-challenger-1p-superboard