|Disabling Internal Hp-41 roms(long)|
Message #1 Posted by Rick Garza on 8 July 2002, 2:35 p.m.
<crazy bizzare esoteric stuff follows>
Is there a way to 'fool' the hp-41 internal roms to remain in sleep on a CV? The idea is an external shadow rom that occupies the entire 64k space and still have the internal regs/mframe stay disabled so as not to draw power or conflict with "now" external instruction fetches.
If it was a C, or an older CV I could cut traces -- but this model has everything neatly buried inside a single chip....and besides its a new challenge.
I know that PWO (PowerOn) is driven by the CPU to disable -- but its also an input for the PowerOnReset circuit. So I wonder can I drive it from the outside? Would this cause the the usual POR? Or with all the RUN/STANDBY/SLEEP smarts would it be just be safely ignored and look for instructions anyway? I know its CMOS and its NEVER ok to have driving pins tied directly together, but I have managed to pull this off it the duty cycle is closely watched....
I have also looked at SYNC but not sure if it would be of any use at all. Looks like its mainly for timing and syncing regs/display/etc and the serial roms respond to the internal addrdecode primarily.
Banking (the Hp scheme) would work only if the 1Lxx internal chiproms are new enough to support it -- and why would they in bank1 and $0000-$3fff? But maybe?
Theres always relocating code up to $8000 but I lose being able to use all those nice roms that have been developed over the years...
The ugliest is to make an external state decoder that watches for long instructions and translates code BEFORE it gets to the cpu, but this could get complicated. It does have the advantage of nice unlimited banking possibilties(not the kind you can deposit--chuckle--).
I ask these questions because I am now committed to making this HP-41CV act as a microCNC controller and will have a plugin that ends in a USB connector.
I am familiar with all the modern stuff. After looking at PICs, Rabbits, ARMs, etc and designing a unit from scratch(been there done that too many times!) the HP-41 is very very attractive and besides its turning into a lot of....FUN! My hats off to the design team, and to think back then I bought a TI!
Who sayz u cant tich an oldog nwe trix?