MLDL
A Machine Language Development Lab (MLDL) is the circuit described in
PPC Journal V9N3. Almost twenty years later, it should be possible to
build one with just a couple of surface-mounted chips. This page is
dedicated to that effort.
I started this discussion in the HP Museum's Forum. The thread is Modern
MLDL / EPROM box for HP41?.
The first step in interfacing to the HP41 is building a connector.
The standard way of doing this is to use an old module. Here is how I did it. You can also use an
HP-IL cable or an 82143 printer cable.
The ROM emulator I built runs on a
Microchip PIC18C252; the rom
image is programmed as a lookup table on the PIC. Here is a picture of the thing on the breadboard,
with a bunch of logic analyzer probes attached to it; it has the HP-IL Development and the PPC ROMs programmed in it (they are both 8K
roms, for a total of 16K).
The circuit is really simple:
The chip on the left is any clock circuit that outputs 40MHz. I use
the EPSON
17 July 2001 - Banked ROMs work
Some modules are 12K; the way they fit in an 8K port is that the upper
4K are banked, and which of the two ROMs is active is controlled by
the ENBANKn instructions (n=1-4). This would have allowed 20K ROMs,
but HP never made them. The Advantage module is an example of a 12K
rom, and it uses the ENBANK1 and ENBANK2 (opcodes 0x100 and 0x180) to
switch.
The next step is to work on power consuption, so that the thing does
not draw 50mA when idle!
