HP--92 Problem

[teenix]

Hi all,

A while ago I read the ROM from a HP-92 but in the process, I broke the ROM 0 chip. Luckily, I was still able to read the data from it, but the chip is not usable because of the wiring that broke away from the die when the case fractured.

I've been using my emulator which runs the HP code I extracted, and I was trying to execute the problem on page 62 of the User Guide.

If I enter the date 8.101977 and press [f][IS,ST] I get an error, but then the emulator fails to work properly. If I enter the MT date first then the IS,ST date, it seems to work.

Tech Talk:

The 97 has the same ROM size as the 92 which is $0000 to $BFFF. The address bits are 12 bits wide so the ACT can only access $0000 to $0FFF. To get around this, a Bank Switch statement is used in the code to switch from Bank 0 to Bank 1 to give the ACT access to $1000 to $1BFF.

Both the 92 and 97 use the same mechanism to return to Bank 0 which is to do a [go to] to any ROM address in the range ($1000 to $13FF), which has no code. So, a go to $1300 instruction causes the next instruction to be fetched from $0301.

The 97 does not use a Bank Switch to get back to Bank 0. However, there is a single Bank Switch instruction in the 92 code in Bank 1 at address $1451. This causes the ROMs to switch back to Bank 0 and the next instruction is fetched at address $0452 which is a subroutine return. I thought this may be the problem, but the 92 has many subroutines that use this particular code, and all other functions appear to work ok when this executes.

I can probably guess that the manual is correct, but if anyone has a 92 and feels like dusting it off for a few minutes and connecting a battery, could you try out the problem by entering 8.101977 [f] [IS,ST] as mentioned in the text. You should see 8.10 on the display

If not, no worries, I'll have to stew on it for a while :-)

cheers

Tony