Xref: utzoo comp.misc:4674 comp.sys.ibm.pc:23072
Path: utzoo!utgpu!watmath!clyde!att!mtuxo!mtgzz!drutx!druhi!neal
From: neal@druhi.ATT.COM (Neal D. McBurnett)
Newsgroups: comp.misc,comp.sys.ibm.pc
Subject: Re: TDD protocol on PC?
Message-ID: <3822@druhi.ATT.COM>
Date: 10 Jan 89 14:54:15 GMT
References: <5604@sdcrdcf.sm.unisys.com>
Organization: AT&T Bell Labs, Denver CO
Lines: 35

in article <5604@sdcrdcf.sm.unisys.com>, darrelj@exec.sm.unisys.com (Darrel VanBuer) says:
| TDDs differ from more common computer communications as follows:
| Baudot instead of ASCII (handle in software with a couple of tables
| and shift state flags) 
| 
| 45 baud (60 WPM in the Baudot 5 level code) instead of 110, 300, 1200,
| 2400 ...  (IBM PC serial I/O chip can be programmed for this, but not
| via the BIOS)
| 
| 5 data bits instead of 7 or 8, no parity (IBM PC serial chip can do it)
| 
| 1.5 stop bits instead of 1 or 2 (any serial I/O chip which does 5 data
| bits usually provides 1.5 stop capability, even those that don't will
| interoperate by programming 2 stop bits since the receiver only needs
| one, and sending 2 instead of 1.5 justs costs 7% of speed)
| 
| Modem uses FSK half duplex signalling which uses frequencies
| incompatible with any other modem (something like 1400 Hz mark, 1800
| Hz space, silent when idle).  I faked it once by using a Motorola
| Modem IC, a fast crystal (to shift freq up) and a couple of inverters
| to fix the data sense [it was a little off spec, but just fine with
| the wide tolerance detectors used at such a slow data rate].
| The deaf community is beginning to use dual standard machines (old
| plus ASCII/Bell 103), but large numbers of existing equipment in the
| hands of many who cannot afford new equipment make this a very slow
| process.  (And the need to change is low for them since even 60 WPM is
| faster than most people can type).

(I included the whole article because I'm cross-posting this to misc.handicap.)

It seems to me that BBS's, on-line library collection databases, etc.
are a great technology for the deaf.  Are there any on-line dial-up services
that interface via TDDs?

-Neal McBurnett, att!druhi!neal