ACT available

[PANAMATIK]

ACT Assembler available!

There are some news about the new ACT, which I want to present here in advance to fill the sometimes boring summer days with something possibly exciting.

I made a completely new approach for extending the original features of the HP-25 calculator. For the first time I manipulated the original HP firmware to add a new behaviour. This could not be achieved with my previous approach by just manipulating the ACT registers. I needed to manipulate the ROM firmware. I don't know if ever somebody tried to write ACT Assembler. It is not very comfortable, the instruction set is rather unusual, compared to todays microprocessors. And there are nearly no scratch registers. Everything is very tight and already outbid. I tried to learn the ACT assembler language to get used to it. For analyzing and manipulating the firmware and entering the mnemonics I had to write a new utility: an ACT Assembler (traditionally either the language is called "Assembler", as well as the compiler for assembling the mnemonics).

Here is a screen shot. You see several windows showing the actual state of the machine. When the program is running all registers will be refreshed at every cycle.



This is not just another HP-25 Emulator, although it is one and all buttons work. Its intention is not to calculate, but to show all registers and to have the possibility to enter new values at any time, even to enter new instructions and to set breakpoints. The assembly mnemonics are exactly the same as presented in Eric's "nonpareil" disassembler. Thanks to Eric for preparing so much.

As a first result I managed to add additional "Continuous Memory" RAM space to the HP-25 calculator and I changed the initialization procedure, which now loads the complete stack X,Y,Z,T and the display format from these new RAM registers, thus making them "Continuous memory". Also the actual program step number and trigonometric mode are preserved. If you switch on your HP-25 you will see the last X Register number in the display with the same decimals when switched off.

And as the second and more tricky result I was able to increase the program size, giving the HP-25 now 98 program steps instead of 49 in one single program. If you press the SST button then you can step forward from 01 to 98 now. The use of additional RAM for the new program space is integrated in the firmware. It was not too difficult.



But there is still some work to do. For now only GTO 00 to GTO 49 instructions are programmable. GTO 98 cannot be programmed, because there is no program code for it. I will have to extend the available one byte program codes and the decoder.

However with these first steps I can already see that it will be possible to integrate very new features, for example adding some more registers and making the Stopwatch or the Print functions programmable. I hope I can make some progress in ACT assembler language, when the summer allows me to have some time for it.

Bernhard