VOGONS


IBM PCjr Problem

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Reply 41 of 45, by ronald_herrera

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Thank you! It working fine.

I'll like to try Microsurgeon, but the last post of this game is that Offset of the segment to the start of the ROM is E600:0000 but what I could understand is that the code has a mirroring effect which the binary file dump needed to be appended some extra bytes (null zeros) to work-around the problem.

Should I edit the binary up to the offset 16384 and split it with 8192 nulls bytes and paste the whole binary code again after the nulls?

Reply 42 of 45, by Great Hierophant

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I forgot Crossfire and added it to the list of known PCjr. cartridge sizes and starting offsets in page two of this thread. Interesting that IBM used small ROM sizes for its games while Activision and Imagic used the larger size.

To make a DOSBox working Microsurgeon dump, you need to do the following.

Start with a 512 byte header with hex values 50 43 6A 72 for addresses 0-3 (PCjr) and the hex value at 1CFh. The rest of the header can be 00. Then, at address 200h, you insert the whole 16K of game code. The code begins with hex EE AA and ends with 13 8B. This takes you to address 4200h. You insert exactly 2000h/8192d (8K) addresses of 00. Finally, you insert the game code again starting at address 6200h.

The resulting image file will be exactly 41,472 bytes (40.5K) in size, no more, no less.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 44 of 45, by ronald_herrera

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Thank you very much for the instructions. I quite follow really well except that I had my doubt on the begging of the code that I had hex: 55 AA, instead of EE AA. At the very last instruction, when said to insert the game code again; I didn't know that you were referring to the same beginning of the code from 200h to the same end before the zero filler starts. Asking myself, what is with the rest of the code before that. But I realized that we were talking about mirroring or repetition of the same code, so I guess the left-over rest of the code was to be cut and effectively was the whole file size you specified (41,472 bytes). Again! Thank you... 😀

Reply 45 of 45, by liqmat

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VileRancour wrote:

With timed=true the joystick's "drift" is related to the cycle count - too low and it drifts to the left, too high and it goes right. Cycles=300 or so works for me.

I know this thread is very old, but I have been pulling my hair out trying to use my joystick with the PCjr carts. This right here did the trick! Thank you!!!

Let me just say Pitfall 2 and Demon Attack on the PCjr are outstanding translations of these titles. When my family owned a PCjr way back in the early 80s I never knew Activision and Imagic made carts for this system. Only until recently did I know they even existed. Amazing what you can still discover about these old systems after all these years.