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The Doors are Open
Nelson M. Sicuro takes first steps to a RAMBox for the HP-42S
Tuesday 3rd of February 2004
After a long period of theoretical speculation - and especially following on J F Garnier's disassembly of the hidded XFCN - Nelson M. Sicuro has now reported a successful addition of RAM to the place holder for additional ROM (i.e. the same ROM place holder used for language adaptation on the HP-17BII). This has also made it possible to make the first real call ever (outside HP labs?) to the XFCN on a real HP-42S. This opens up future possibilities for machine code programming on the HP-42S, especially longed for are functions for serial I/O, but also simpler functions like a programmable FAST mode for Rev B and C calcs might also be useful.
This is Nelson's description of his modification:
"The rewiring is very simple, cut two jumpers (the only with a drop of solder), and get the /WE from the RAM chip, the other is getting the A14 from a side of one of the jumpers and connecting to anoter one (see picture)."
This modification was made using a 32K RAM chip (Hitachi HM62256LFP-8T) giving a RAM that is mirrored once in the 64K ROM area ($20000 to $3FFFF).
(Click on image for large version)
References:
HP-42S: New Facts by J-F Garnier on www.hpmuseum.com
Nelson M. Sicuro takes first steps to a RAMBox for the HP-42S
Tuesday 3rd of February 2004
After a long period of theoretical speculation - and especially following on J F Garnier's disassembly of the hidded XFCN - Nelson M. Sicuro has now reported a successful addition of RAM to the place holder for additional ROM (i.e. the same ROM place holder used for language adaptation on the HP-17BII). This has also made it possible to make the first real call ever (outside HP labs?) to the XFCN on a real HP-42S. This opens up future possibilities for machine code programming on the HP-42S, especially longed for are functions for serial I/O, but also simpler functions like a programmable FAST mode for Rev B and C calcs might also be useful.
This is Nelson's description of his modification:
"The rewiring is very simple, cut two jumpers (the only with a drop of solder), and get the /WE from the RAM chip, the other is getting the A14 from a side of one of the jumpers and connecting to anoter one (see picture)."
This modification was made using a 32K RAM chip (Hitachi HM62256LFP-8T) giving a RAM that is mirrored once in the 64K ROM area ($20000 to $3FFFF).
(Click on image for large version)
References:
HP-42S: New Facts by J-F Garnier on www.hpmuseum.com