IBM PCjr. Modem - What can I do with it?

Hardware questions and modifications

Re: IBM PCjr. Modem - What can I do with it?

Postby GHiero » Thu Feb 13, 2014 3:46 pm

geoffdaddy wrote:I have used 300bps over a cell phone call before, so I imagine if you're using any properly classified/shaped VoIP service through a carrier class network then it should be more than adequate for 300 bps.

I suppose it's also possible that whatever system's modem you are connecting to has crappy support for Bell 103 compatibility since it's mostly vestigial support at this point, or that the PCjr's modem really is That Bad. ;)

FWIW, back in the day a friend of mine had a Tandy 1000EX and bought the internal PLUS card 1200 bps modem for it. Almost NO BBS (or Telenet/Tymnet/Sprintnet for that matter) supported 1200bps mode correctly and/or the firmware on the modem was too persnickety to work, so he was relegated to connect at 300 bps most of the time.


It definitely sounds like I need some better software. Trouble is finding it. Telix 3.51 does not want to work with the PCjr. keyboard.

Oh, I have a Tandy 1200 baud modem for my Tandy 1000 SX, which probably was the equilavent to the PLUS Modem in your friend's EX. That one seems to work decently enough with Telix.
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Re: IBM PCjr. Modem - What can I do with it?

Postby Brutman » Thu Feb 13, 2014 10:01 pm

- Any voice over IP line should be able to handle a 300 bps modem. There is a lot of compression involved but 300bps is not stressing anything - FAX machines routinely run over VoIP. You should investigate setting your VoIP device up so that it gives more bandwidth to your calls; look for a FAX machine mode setting. (Ooma has this. I'm sure others do too.)

- There is probably nothing wrong with your modem or it's implementation of Bell 103. But your VoIP settings are probably clobbering the sound quality and making connections difficult. You are also finding that some BBS systems just don't want to deal with such a slow device; telephone lines used to cost money and it was common to have separate lines for slow speed devices so that people would not have all of their lines tied up by that class of device. You might try contacting the owners of those BBS systems to get them to life the restrictions.

- A lack of ANSI emulation is a usability problem. But there are plenty of programs you can download that have ANSI emulation, and are not written in interpreted BASIC. Do some searching for programs like Qmodem, Telix and Procomm and try a few out. If Telix doesn't work there are many others. There are dozens and dozens of shareware sites on the internet that host these things. I recommend Procomm 2.4.3 and I have PC-Talk available for download right from this site.

- 64KB is not a problem or a limit - it is not relevant. Characters come in through the modem and get displayed on the screen. The screen is your buffer. Interpreted BASIC is slow, but certainly fast enough for 300 bps operation. Memory limits are not an issue.
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Re: IBM PCjr. Modem - What can I do with it?

Postby GHiero » Fri Feb 14, 2014 9:08 am

I found ProComm 2.4.3 and will try that
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Re: IBM PCjr. Modem - What can I do with it?

Postby GHiero » Sat Feb 15, 2014 7:33 pm

So I am trying to use ProComm 2.4.3, and it is obviously designed for a Hayes modem. I go to the setup screen and change the Modem options as follows :

Initialize - format 4 (should set modem to 8-N-1 operation)
Dial command - dial w
Hangup - hangup

When I try to dial a number, I set the baud and operation rate for the number, it will say Dialing and echo the command, and nothing happens. I tried calling myself and nothing happens. What am I missing?
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Re: IBM PCjr. Modem - What can I do with it?

Postby geoffdaddy » Mon Feb 17, 2014 1:27 pm

GHiero wrote:So I am trying to use ProComm 2.4.3, and it is obviously designed for a Hayes modem. I go to the setup screen and change the Modem options as follows :

Initialize - format 4 (should set modem to 8-N-1 operation)
Dial command - dial w
Hangup - hangup

When I try to dial a number, I set the baud and operation rate for the number, it will say Dialing and echo the command, and nothing happens. I tried calling myself and nothing happens. What am I missing?


Are you missing the command's terminating <cr>? Maybe that's it. If you type it directly does it work?
PCjr: 10MB RACore 01 hard drive expansion, Hotshot 640kB RAM expander, optical mouse, Xircom PE3, speech sidecar.
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Re: IBM PCjr. Modem - What can I do with it?

Postby GHiero » Tue Feb 18, 2014 12:18 am

Okay, so here is what I need to do :

♫ initialize, format 4 [CR]
♫ dial w15551234567 [CR]
♫ hangup [CR]

The ♫ is the default command character that tells the modem that what follows is a command and not data. The [CR] is the carriage return required for the command to be sent.

My problem is that I do not know how to manually enter commands in Procomm and the modem setup does not allow entry of the ♫ character (either by Control N or Alt 14).
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Re: IBM PCjr. Modem - What can I do with it?

Postby geoffdaddy » Tue Feb 18, 2014 7:53 am

I believe in procomm that control codes are prefixed by ^, so a carriage return is ^M. Try ^N for your escape code too.
PCjr: 10MB RACore 01 hard drive expansion, Hotshot 640kB RAM expander, optical mouse, Xircom PE3, speech sidecar.
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Re: IBM PCjr. Modem - What can I do with it?

Postby geoffdaddy » Tue Feb 18, 2014 8:12 am

I should not though that the ^ thing will probably only work where you're entering the modem unit string and dialing prefix, not on the normal terminal screen.
PCjr: 10MB RACore 01 hard drive expansion, Hotshot 640kB RAM expander, optical mouse, Xircom PE3, speech sidecar.
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Re: IBM PCjr. Modem - What can I do with it?

Postby GHiero » Tue Feb 18, 2014 12:43 pm

That worked. Now I was finally able to connect to a BBS: In Procomm the commands should look like this on the modem setup screen :

^N initialize, format 4 ^M
^N dial w
^M
^N hangup ^M

I find that the 7-E-1 format gives more reliable results than 8-N-1. With the 8-N-1 format, the modem will not reliably echo commands sent to it and will also show more garbage characters.

With procomm, I have this issue where the characters I type repeat themselves. For example, if I type 24, it will show up as 2424. If I were to enter my user name, Great Hierophant, it would appear GGrreeaatt HHiieerroopphhaanntt. Fortunately the BBS I tried displayed Great Hierophant in response to my text entry, but it is rather annoying. The only way I can input text reliably is if I press one key, wait for the double key, and then press another key, etc. Any advice on how to deal with this?
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Re: IBM PCjr. Modem - What can I do with it?

Postby Brutman » Tue Feb 18, 2014 1:15 pm

Do you have local echoing turned on in Procomm?
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