Starting a PCjr coding project, need advice

Discussions on programming older machines

Starting a PCjr coding project, need advice

Postby Trixter » Mon Sep 01, 2008 11:51 am

I know that in the past, Mr. B has coded on a 386-40 and tested his results on a PCjr. I am going to start a very large PCjr programming project, but this time I will be using the graphics and sound on the PCjr and therefore can't test on a 386. I also can't program directly on the PCjr since all of my PCjrs have a single floppy and that's not enough room for the build environment (which consists of data files, editor, compiler, and source code). To make things more interesting, I'm going to co-develop this with a friend who also has a PCjr. So I figure I have two choices:

  • Try to program on a Tandy 1000 (which can easily take a hard drive) or emulator like DOSBox
  • Try to attach larger storage to the PCjr so that I can code on the actual machine

My questions:

  • What is the magic combination to getting a ZIP drive working on a PCjr? I have tried several versions of GUEST and DOS (I quickly found out that DOS 5.0 or later was a requirement, it won't start up properly in 3.x) but have had no success. Is there a boot disk someone can prepare for me that works for them?
  • Using a real Tandy 1000 or emulator is slightly more appealing because there's more power under the hood, but what are the major differences between programming the Tandy 1000 vs. the PCjr? ie. Can I code for PCjr and it should magically work on Tandy and vice-versa, or is it not that simple?
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Re: Starting a PCjr coding project, need advice

Postby Brutman » Mon Sep 01, 2008 12:04 pm

What's the programming environment? In my case Turbo C++ is very large (beyond floppies) and it requires extended memory to run, so it will never run on a Jr. If your issue is just disk space that is easily corrected. Options:

  • Parallel port IDE drive
  • Parallel port to SCSI adapter with SCSI drive
  • Parallel port Zip drive with PalmZip drivers
  • Parallel port Zip drive with Iomega Guest. I think this works on my NEC V20 equipped machine. I used to think that it worked on plain 8088s, but I can't recreate it.

I think that if you pick the right graphics mode on the Tandy that it will work on the Jr. 320x200 in 16 colors, 160x200 in 16 colors, and 640x200 in 4 colors should work, with multiple pages too. Do a simple test to verify. The Tandy was designed to be compatible with all of the Jr modes so you should be fine if you stick to the Jr modes.

Just curious - what are you guys doing, and is it with anybody I know?
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Re: Starting a PCjr coding project, need advice

Postby Jim Thomson » Mon Sep 01, 2008 3:32 pm

The driver for the zip drive for the PCjr is
PALMZIP.SYS
You can get it off of the internet.
It works in all versions of dos. For Dos 2.1 it splits a zip disk into three partions.

Hope this helps.
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Re: Starting a PCjr coding project, need advice

Postby Trixter » Mon Sep 01, 2008 7:16 pm

Brutman wrote:If your issue is just disk space that is easily corrected. Options:

  • Parallel port IDE drive
  • Parallel port to SCSI adapter with SCSI drive
  • Parallel port Zip drive with PalmZip drivers
  • Parallel port Zip drive with Iomega Guest. I think this works on my NEC V20 equipped machine. I used to think that it worked on plain 8088s, but I can't recreate it.


Looks like I'll have to dig up some SCSI enclosures (I think there are a few at work) and finally get one of those adapters. For the benefit of my fading memory as well as others who might want to search for some, can you list one or more parallel-port SCSI adapters by make/model so that I can start searching ebay for them? There's one there now (110284004448) but it appears to only come with W95 drivers and support 486s and higher.

I can confirm 80286 is required for GUEST; I tried it on a 10MHz NEC V30 and no dice, but on a GRiD 286 it worked fine.

Just curious - what are you guys doing, and is it with anybody I know?


David Valentine (Polaris / Northern Dragons) and I are tossing around the idea of doing a PCjr demo. (as in "demoscene" demo) There are some real hurdles (128KB RAM on a "stock" PCjr which is our target, slow memory speed) and also some advantages (sound chip, multiple video pages) so it's an interesting idea.

We both own PCjrs (mine has 640k and NEC V20, his has 512K and 8088, both with monitors and single floppy drive) but trying to come up with a decent development environment has been troublesome.
You're all insane and trying to steal my magic bag!
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Re: Starting a PCjr coding project, need advice

Postby Jim Thomson » Tue Sep 02, 2008 5:05 pm

The best( i.e. fastest) parallel to scsi adapter is the Bridge 888. They show up infrequently on eBay.
The Trantor T-348 is a little bit slower but is more readily available.
The Trantor/Adaptec A-358 is slower than the T-348 so it should be avoided.
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Re: Starting a PCjr coding project, need advice

Postby Brutman » Tue Sep 02, 2008 5:10 pm

Hi Jim!

Also to consider ...

  • The Trantor/Adaptec 338
  • Any 'clone adapter' based on the above, such as the NEC CD-ROM connection kits

Forget the Bridge 888 .. I haven't seen one for sale in years. They are awesome. I think it is based on the Shuttle EPST chipset, so I would be willing to try an EPSA or EPST based adapter.


Mike
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Re: Starting a PCjr coding project, need advice

Postby Trixter » Tue Sep 02, 2008 5:19 pm

Any 'clone adapter' based on the above, such as the NEC CD-ROM connection kits


I found one, but the only driver is Windows 95. Is there a real-mode driver for the above online somewhere?
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Re: Starting a PCjr coding project, need advice

Postby Jim Thomson » Fri Sep 05, 2008 5:07 am

http://support.nectech.com/advmedia/dri ... sidrvr.htm

Try this site it has the SCSI drivers for the nec adapters.
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Re: Starting a PCjr coding project, need advice

Postby Trixter » Fri Sep 05, 2008 9:55 pm

But will the drivers work with a SCSI hard drive, or only CDROMs?
You're all insane and trying to steal my magic bag!
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Re: Starting a PCjr coding project, need advice

Postby Trixter » Sat Sep 06, 2008 1:47 am

I just had another thought: Before starting, I should whip up a program that does VERY PCjr-specific things, like 160x200x16 graphics on two or three video pages, 3-voice audio, a little IRQ 5 (if I read the techref correctly it's a real Video IRQ!), etc. and then run under DOSBOX and also on a Tandy to see if those are acceptable development environments.

Has anyone messed with a PCjr really really deep? I ask because, since the VGA refreshes the DRAM, timer 1 is now free, but the techref says it's programmed by the BIOS to handle "disk motor timing". If I screw with timer 1, will I screw up disk drive handling if I don't restore it properly?
You're all insane and trying to steal my magic bag!
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