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PCJr. Option ??

G

Great Hierophant

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I have some questions about the various options for the PCjr.

IBM 128KB Memory Expansion - There are dipswitches on this card, does anyone have the settings? How far can you upgrade the memory with these particular cards? 256, 384, 512, 640, 736K?

IBM Power Expansion Unit - I hear that these cards can power about three sidecars a piece. If you have six or seven other IBM sidecars, would you need one or two of these sidecars?

IBM Attachable Joystick - How long is the joystick cable?

IBM Internal Modem - Can this Modem, with its non-Hayes compatible command set, be of any use?

Finally, what is the best way to get data from a modern PC to the standard PCjr? One way is to have a 360KB 5.25" drive (even the PCjr.'s drive as drive B) in the not-too-modern PC and write software to disks. Any other method like direct parallel or null modem would require custom software to be loaded on the jr. first.
 
IBM PCjr Memory Sidecar settings

IBM PCjr Memory Sidecar settings

IBM PCjr memory sidecar settings (Genuine IBM only)

1st 128K Expansion: 1 On, 2 Off, 3 Off, 4 Off
2nd 128K Expansion: 1 Off, 2 On, 3 Off, 4 Off
3rd 128K Expansion: 1 Off, 2 Off, 3 On, 4 Off

4th 128K Expansion: Not documented, but follow the pattern.

IBM only allowed for 3 expansions, for a total of 512K. You can easily add a forth to get to 640K.

To get to 736K you need to make a modification to the addressing lines on the card.

Instead of using multiple sidecars it makes more sense to upgrade the 64Kx1 chips in each sidecar to 256Kx1 chips. The modification is tedious, but not complicated. This will also reduce the power draw quite a bit.
 
Power Expansion Sidecar: This is equivalent to another 30 to 40 watts of power. The rule of thumb was 3 additional sidecars, but some sidecars like the Cluster sidecar are very power hungry and will probably consume a power sidecar by itself.

An undocumented secret of the Power Expansion sidecar is that it provides -12V on one of the reserved pins.

The joystick has about a 5 foot cord. You can attach two.

The IBM Internal modem is a 300 bps modem based on a Novation model. It is perfectly usable - as usable as any other modem of the era. The non-Hayes AT command set presents some problems, but you can dial send and receive data just like with any other modem.

If you need to get data to and from a PCjr you have some options:

  • Serial cables and null modem adapter. Use a comm package on both sides and send binary files using Xmodem, Ymodem, Zmodem, Kermit, etc.
  • Diskette. Low density diskettes only. (3.5 720KB will work with DOS device driver support, as the floppy controller can drive these.)
  • Zip drive or other exotic device - these can be driven from the parallel port, if you have a parallel port
  • Network - I use a parallel-port to Ethernet adapter to put my PCjr on the network!
  • Others ...

None of these data transfer methods is really specific to the PCjr - they apply to any older machine with incompatible diskette media.

For more details take a look at http://www.brutman.com/PCjr - most of this is well documented there.
 
mbbrutman said:
If you need to get data to and from a PCjr you have some options:

  • Serial cables and null modem adapter. Use a comm package on both sides and send binary files using Xmodem, Ymodem, Zmodem, Kermit, etc.
Click to expand...
You can also use a parallel cable and the InterLnk / InterSvr utilities that come with DOS 6.x. This runs much faster than data transfer through a serial cable (I used "LapLink" years ago for that)... but once I got a parallel-port Zip drive, I forgot all about data transfer through serial/parallel cables or floppy disks. With 100 MB on one disk, you can even use it as a makeshift "hard drive", although the transfer rate isn't as fast as a real one.

However, Iomega's DOS driver requires at least a NEC V20 CPU, as it uses real-mode 286 instructions which don't work on a standard 8088 or 8086. I hear that third-party Zip drive drivers are available which will work on an 808x, though.
 
A few notes:

  • Older Iomega drivers for the Zip work fine on an 8088. I've run the Iomega drivers on an XT with an 8088.
  • Palmzip is the name of the 3rd party driver you are referring to.

There are plenty of old threads here that describe Zip drives on an 8088.

I've never used LapLink because DOS 6 doesn't run happily on a Jr - it takes some patching.
 
The PCjr. is only designed to support one floppy drive and will not support a second one without a third party product. Why not a 720KB drive? It is a bit unfortunate that the system BIOS will only recognize it in 360KB mode, so 720KB booters probably will not work. With mounting kit it should fit inside the case. However, the zip drive may be the best option to use.
 
You could also switch to a Tandy 1000, and get PCjr sound/graphics compatibility with much more standardized hardware support (real ISA slots!). ;)
 
The modification to the controller to support a 2nd drive is well known. And even if you just swapped the original drive for a 720KB drive, you could use it as a 360KB drive (drive A:) and with a DOS device driver (driver.sys) as a 720K drive (drive B:) with no modifications.

I'd put a 360K drive in a machine that has a 1.44MB floppy drive in it too. And preferably that machine is running DOS, Linux or an early version of Windows so that you can have network connectivity. An old machine is kind of hard to work with unless you have a 'mothership' system like this.

If you can't do that, the serial port and a null modem cable will work. Procomm 2.4.3 was my favorite file transfer program. The solution assumes that you have DOS diskettes and Procomm 2.4.3 (or an equivalent) already. If you don't, a fairly crude BASIC program can get you enough loaded from the remote system to get you started.
 
When my sister had a PC jr back in the 80's I found docs that described how to modify a 128K sidecar to make it a 512K sidecar as well as docs to modify the original FDC to add a 2nd floppy drive. I did both mods on my sister's PC jr. Neither were very difficult.

The 128k sidecar used 16 64k chips the mod required replacing the 64k chips with 16 256K chips. There were a couple of other mods to allow the sidecar to address 512K.

Here's a link for the instructions to add a 2nd floppy: http://www.micro-zone.com/HCMfloppy.html
 
I'll make a strong case for the XT-IDEjr :)

By the time one purchases sockets @ 0.10 apiece, memory chips at roughly 0.99 apiece, and then takes the time to snip, desolder, and solder in new sockets, you've a few hours and about $30 or so into the project. Why not put take that $30, double it, and just about walk away with an XT-IDEjr that gives you the RAM, modern hard drive interface (i.e. use a CF->IDE and have easy, no hassle transfers), 736kb, and all through the PCjr power supply?

If you go that route, ping me... I might have a spare sidecar I could donate to ya for the cost of shipping to give you the shell.
 
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