Hello,

I am trying to interface with an ancient (from 1980!) PMOS ROM that uses -9V as logic low and 0V as logic high. Does anyone know of a way to do bi-directional voltage level conversion to use this with a more common 5V microcontroller?

Thanks!
-Skot

 

What speed are we talking about here?

Do you have a datasheet of the ROM?

 

Clock frequency is 100-200 kHz.

Datasheet: http://www.skot9000.com/data/tms6100.pdf

thanks!

 

Also, BTW, I'm pretty sure in section 3.2 of the datasheet there is a small typo. Vdd should have a range of -8.3V to -9.7V (NOT -8.3V to 9.7V)

 

The simplest way to start is ground the -9V Vdd and connect ground to +9V.

That way at least the signals are above ground, logic zero is zero, and you only have to divide or scale up the ones.

 

Awesome! I think this is the right idea. It looks like will even be able to use regular 5V logic this way, albiet inverted.

thanks!