Power on reset
eZ80 for RC2014™ and compatible backplanes
An eZ80 CPU Module that works within the RC2014™ ecosystem
11 Aug 2024
One issue I hit when I was attempting to port the V9958 driver code (TMS9918 compatible driver), was an apparent intermittent fault. After a few frustrating hours, I figured out that the V9958 was not being ‘reset’ on power up - and could not be initialised correctly by the CPU.
I think the V9958 is very fussy on requiring that its held in RESET during power-up. If not, it will be in a state that does not seem to be correctable in software.
I realised that I forgotten to include a Power-On-Reset circuit in my design.
A quick work around is to press the RESET button on the backplane after initial powering on the kit.
The original RC2014 Dual clock module does include a Power-On-Reset circuit, but this module is not required for the eZ80 Interface module as it has its own high speed clock on board.
I have drafted a new PCB design that includes a Power-on-Reset facility; this should ensure the whole system is held in RESET state for a few milliseconds when its initially powered on, and allow the V9958 to initialise itself correctly.