Paratrooper on PCjr

Software related questions

Paratrooper on PCjr

Postby Brooklyn » Tue Feb 10, 2015 9:37 pm

Hi guys, has anyone had any luck getting the classic game "Paratrooper" running on a PCjr? The game starts, but quickly the title screen and in game graphics go scrambled. The game still plays and responds to controllers. I figure it is one of those games the PCjr doesn't run, but maybe there is a work around?

IMG_4506.jpg
(444.45 KiB) Not downloaded yet
Brooklyn
 
Posts: 2
Joined: Sun Jan 11, 2015 7:07 pm
Location: Chicago, IL

Re: Paratrooper on PCjr

Postby Trixter » Tue Feb 10, 2015 10:20 pm

I haven't looked at it but it's probably similar to the issue described here: viewtopic.php?f=3&t=442&start=10#p3181

If you aren't adept at patching .com files, I could take a look at it.
You're all insane and trying to steal my magic bag!
Trixter
 
Posts: 495
Joined: Mon Sep 01, 2008 12:00 am
Location: Illinois, USA

Re: Paratrooper on PCjr

Postby Brooklyn » Wed Feb 11, 2015 10:15 pm

I have no idea how to patch a .com file...:)
Brooklyn
 
Posts: 2
Joined: Sun Jan 11, 2015 7:07 pm
Location: Chicago, IL

Re: Paratrooper on PCjr

Postby Trixter » Thu Feb 12, 2015 10:12 am

I'll put it on my list, but it could be a few days as I need to set up my PCjr debugging rig.
You're all insane and trying to steal my magic bag!
Trixter
 
Posts: 495
Joined: Mon Sep 01, 2008 12:00 am
Location: Illinois, USA

Re: Paratrooper on PCjr

Postby Trixter » Thu Feb 12, 2015 11:55 am

Actually, I had a quick look over lunch and this seems to be, luckily, a simple patch. Paratrooper makes the same mistake Elite did, assuming it knew what bit 2 was used for in port 61h. On a PCjr, this bit controls whether or not the video mode is text or graphics, and sets it incorrectly on a PCjr. Greg Kuperberg (author of Paratrooper) can be excused for this mistake because no other PCs or clones existed when he wrote the program :-)

To fix this, you can patch where it is doing that. Type "debug trooper.com" (without the quotes) at a DOS prompt, and then type this:

Code: Select all
s 100 ffff b0 4f ENTER ("ENTER" means hit the enter key.  This will search your copy of paratrooper for the wrong code and return the address it found it at.  Note the hex number AFTER the colon.)
e 12CD ENTER (replace the number "12CD" with one MORE than what the search returned.  So if the search returned 3215, you would use 3216; if it returned 115D, you would use 115E; etc.)
4b ENTER (this replaces the wrong value "4f" with "4b" which has the bit set properly for graphics mode on the PCjr)
w ENTER
q ENTER


This should make the game playable on a PCjr. You can find debug.com on one of your DOS disks.

I've attached a sample debug session screenshot you can refer to. Let me know if you run into trouble.
Attachments
patch paratrooper.png
(2.78 KiB) Not downloaded yet
You're all insane and trying to steal my magic bag!
Trixter
 
Posts: 495
Joined: Mon Sep 01, 2008 12:00 am
Location: Illinois, USA


Return to PCjr Software

Who is online

Users browsing this forum: No registered users and 1 guest

cron