[Diy_efi] Re: What type masked ROMS on early motronic ecu's

[Jeffrey Engel]

Phil,

Thanks for the update.  I should have known better
than to trust my memory.

Jeff
--- Phil Hunter <diy-efi-d at t-n-e.com> wrote:
> Jeff wrote:
> > ... has quite different '0' and '1' thresholds. 
> Try driving
> > it with HC family logic, TTL won't work.
> 
> TTL can work. "classic" CMOS has a logic threshold
> at one half
> of the power supply, if the supply is 5V then the
> threshold is
> 2.5V. "classic" TTL has a minimum logic high output
> of 2.4V,
> adding a 4.7K pullup resistor is enough to have TTL
> drive CMOS.
> I'd be surprised if a prom programmer wasn't
> designed to be
> compatible w/ both TTL & CMOS EPROMs.
> 
> rgds,
> philh
> (digest)


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