My Midi controlled VCF module

[Ingo Debus]

> Jeroen Proveniers wrote:
[Power-on reset circuit]
> A resistor and capacitor will suffice I think. Otherwise, a MAX690
> (unfortunatly expensive) will do the job nicely.

I bought a kit with a 80C535 (from Wickenhaeuser) which has a capacitor-only
(10uF, pullup resistor is on chip) power-on reset circuit. This worked
fine, but then, the SRAM in this kit is not battery backed-up. I wanted
the SRAM data non-volatile, so I added a battery and a simple circuit to
keep /CE of the SRAM high while power is off. I seems the processor
writes some random data into the SRAM during power-down. The SRAM data
were untouched when the reset button (parallel to the 10uF cap) was held
down when the power was turned off.
The solution was simple: I replaced the cap with a TL7757. It fits in
nicely because it's a 3-lead TO92. Only one additional wire (for Vcc) required.

Ingo