emma@sbsvax.UUCP (Martin Emmerich) (06/05/89)
In article <692@flatline.UUCP>, erict@flatline.UUCP (J. Eric Townsend) writes: > I'm looking for leads/pointers/sources of modems that will work > with the French Minitel (U.S. Videotel in the United States). These > modems use a wierd 75bps one way/1200bps the other way protocol. > I would prefer that they run off a serial port, but if you only > know of ones that are PC internal modems, that'd interest me as well. At the CeBit Fair, Hannover, West-Germany, I bought an SmartLink 2400A external Modem. List price was 293$, I think. It supports these strange split-speed modes in _both_ ways ( isnt it V.23 ? ), V.21, V.22, V.22bis and 300+1200 bps Bell. The 2400A is manufactured in Taiwan by one of the companies who have built the SmarTeam modems. They now have separated into Team and SmartLink. Rumors say it would be possible to use a normal V.22 modem for split-speed. You only had to lengthen every bit into 16 bits ( = 1200 / 75 ) by software. But I never tried it. It is said that someone had done it sucessfully. CU, /\/> / ,--- / | Snail: Hangweg 9 / / _ __-/- o _ /-- __ __ _ __ o _ /_ | D-6601 Buebingen / /_/_(_/(_/(_(_/ ( /___//(_//(_(/_/(_(_(_/ ( | Voice: +(49)6805/8299 ---------------------------------------------------+------------------------- X.400: emma@sbsvax.informatik.uni-saarland.dbp.de | Z-Net: aniel@eiko.zer
ch@maths.tcd.ie (Charles Bryant) (06/08/89)
In article <762@sbsvax.UUCP> emma@sbsvax.UUCP (Martin Emmerich) writes: }In article <692@flatline.UUCP>, erict@flatline.UUCP (J. Eric Townsend) writes: }> I'm looking for leads/pointers/sources of modems that will work }> with the French Minitel (U.S. Videotel in the United States). These }> modems use a wierd 75bps one way/1200bps the other way protocol. } }Rumors say it would be possible to use a normal V.22 modem for split-speed. You }only had to lengthen every bit into 16 bits ( = 1200 / 75 ) by software. But I }never tried it. It is said that someone had done it sucessfully. It is definitely not possible. The 1200/75 standard is V.23 (which is quite popular in Europe). This uses a Frequency Shift Keyed modulation scheme. The V.22 standard uses Phase shift modulation (same as Bell 212A). -- Charles Bryant. Working at Datacode Electronics Ltd. (Modem manufacturers)
paul@csnz.co.nz (Paul Gillingwater) (06/15/89)
In article <874@maths.tcd.ie> ch@maths.tcd.ie (Charles Bryant) writes: +In article <762@sbsvax.UUCP> emma@sbsvax.UUCP (Martin Emmerich) writes: +}In article <692@flatline.UUCP>, erict@flatline.UUCP (J. Eric Townsend) writes: +}> I'm looking for leads/pointers/sources of modems that will work +}> with the French Minitel (U.S. Videotel in the United States). These +}> modems use a wierd 75bps one way/1200bps the other way protocol. +} +}Rumors say it would be possible to use a normal V.22 modem for split-speed. You +}only had to lengthen every bit into 16 bits ( = 1200 / 75 ) by software. But I +}never tried it. It is said that someone had done it sucessfully. + +It is definitely not possible. The 1200/75 standard is V.23 (which is quite +popular in Europe). This uses a Frequency Shift Keyed modulation scheme. The +V.22 standard uses Phase shift modulation (same as Bell 212A). V.23 is a CCITT standard that was developed by British Telecom as a low-cost solution for videotext applications. It uses FSK as opposed to DPSK as correctly pointed out by Charles. V23 also allows for a 600 bps fall-back on the receive channel. The problem with most split-speed modems is that a normal PC does not have a split-speed serial interface. However, a clever programmer here in New Zealand has written software that SIMULATES the 75 baud on the DTE by playing with DTR. And it works! However, if you don't want to dial into a NZ BBS to obtain that, then you'll need to obtain a modem which does speed conversion on the TX channel. Note that V23 is a half-duplex protocol - that means that it can be turned around to give 1200 bps TX and 75 bps RX, e.g. for uploading to a BBS. I still get people who try to upload at 75 bps though... :-( -- Paul Gillingwater, Computer Sciences of New Zealand Limited Bang: ..!uunet!dsiramd!csnz!paul Domain: paul@csnz.co.nz Call Magic Tower BBS V21/23/22/22bis 24 hrs +0064 4 767 326
GPWRDCS@gp.govt.nz (Don Stokes, GPO) (06/26/89)
In article <762@sbsvax.UUCP>, emma@sbsvax.UUCP (Martin Emmerich) writes: > Rumors say it would be possible to use a normal V.22 modem for split-speed. You > only had to lengthen every bit into 16 bits ( = 1200 / 75 ) by software. But I > never tried it. It is said that someone had done it sucessfully. Not a prayer. The modulations, carriers and baudrates are different. V22 actually runs at 600baud, two bits per baud using phase modulation. V23 is normal FSK, at 1200baud. What you may have heard of is multiplying bits to produce a 75bps back channel for a V23 modem on a DTE that does not support split speeds - although start and stop bits would complicate the issue more than slightly - it would be like communicating over a noisy line. Remember that there are 10 bits to a transmitted byte (assuming 8 bits, no parity or 7 bits with parity, and one stop bit). Don Stokes, Systems Programmer / / Domain: don@gp.govt.nz Government Printing Office, /GP/ PSImail: PSI%0530147000028::DON Wellington, New Zealand / / UUCP: ...!munnari!vuwcomp!windy!gpwd!don -------------------------------------------------------------------------------- There is always one item on the screen menu that is mislabelled and should read "ABANDON HOPE ALL YE WHO ENTER HERE".
GPWRDCS@gp.govt.nz (Don Stokes, GPO) (06/26/89)
In article <48@csnz.co.nz>, paul@csnz.co.nz (Paul Gillingwater) writes: > However, a > clever programmer here in New Zealand has written software that SIMULATES > the 75 baud on the DTE by playing with DTR. And it works! Just nit picking again (do I do anything else?), but SJ's little 1200/75 ditty does not use DTR for back channel transmission - it uses DTR to dial the modem and the break signal generation on the UART to generate the 75bps channel - effectively lowering and raising the transmit line on command. The programs that use it (correct me if I'm wrong Paul) are: DIAL The original - pulse dials numbers using DTR and handles split speeds. I'm not sure how this is used. TARG Comms program written around DIAL. HAYES Hayes emulator for dumb modems, written by another local chap using DIAL's baudrate splitter and pulse-dialer. Sends responses for loss of carrier, connect etc. Requires patches to comms software - patches exist for Procomm and Telix (I forget which versions). All these are for MS-DOS systems. Don Stokes, Systems Programmer / / Domain: don@gp.govt.nz Government Printing Office, /GP/ PSImail: PSI%0530147000028::DON Wellington, New Zealand / / UUCP: ...!munnari!vuwcomp!windy!gpwd!don -------------------------------------------------------------------------------- A bad sector disk error occurs only after you've done several hours of work without performing a backup.