|Emulated HP-41 ROM pacs... at last!|
Message #1 Posted by Diego Diaz on 10 Oct 2003, 7:56 p.m.
Yes, it works. A 28 pin PIC18F252 with the Stuctural Analysis module ROM image is connected to my HP-41 right now... and, of course, it's correctly recognised and fully operative.
I've used the PIC code from John Ioannidis' 18C252 PAC with almost no modifications. Great job John!!
The next step is to place the SOP version of the chip inside a standard module enclosure. It needs nothing but the PIC, one diode and a Xtal to run.
Several issues are still pending though:
1) The device needs 6.5 - 7.5mA wich is a pretty low figure, but... (this are the bad news) it keeps on running even when the calc is off... Still working on that, and have found a simple method to switch the PIC off but... (there's always a "but"... :-( paradoxically this method is only useful when the batteries are weak, as it needs a sensible voltage difference between BAT and V+ lines, and that doesn't occur with fresh batteries. Your comments or ideas are welcomed.
2) As the PIC holds 5 pages (4k words x 10 bits), the B3 and B4 lines can not be used to map the module according with the port number it is connected to. Of course you can sacrifice 3 pages and map the device into the correct port, but I think this small win shouldn't justify the loss.
3) Early 41's introduce two inverted pulses in the SYNC line at phases 49 and 53. This behavior fools the PIC code, thus it can not be used with those early machines.
4) The code is supposed to handle bankswitching between banks 1 and 2 (I haven't try this yet), so modules with pages in banks 3 and/or 4 can not be burned. IIRC only the HEPAX module uses this feature, but may be others. Nevertheless I think this could be implemented with very little code modification.
5) Last, but, again, not least, I have no other modules to cannibalize and experiment with!!
Your comments, corrections, suggestions, and support will be of great help. If you want to mail me please remove the NOSPAM garbage from my address above.
Constructive critics are also welcomed, please send the destructive critics to my ex-wife (she's an expert in that matter ;-).
Kind regards from the Canary Islands.
Edited: 10 Oct 2003, 8:06 p.m.