d5kwedb@hacke9.dtek.chalmers.se. (Kristian Wedberg) (07/13/89)
I've written a Videotex program (Prestel type) for the Amiga, a kind of communication program. Trouble is, here in Sweden some folks have 75/1200 modems instead of the more normal 1200/1200. As it is, I have no idea how to support 75/1200, or indeed, if it's at all possible. Altzo, is it possible to transmit 75 bit/s and receive 1200 bit/s over the serial port? At the same time? Or would you need some kind of transformer? wonders kitte d5kwedb@dtek.chalmers.se
gert@targon.UUCP (Gert Kanis) (07/14/89)
In article <539@vice2utc.chalmers.se> d5kwedb@hacke9.dtek.chalmers.se (Kristian Wedberg) writes: >I've written a Videotex program (Prestel type) for the Amiga, a kind of >communication program. Trouble is, here in Sweden some folks have 75/1200 > >As it is, I have no idea how to support 75/1200, or indeed, if it's at all >possible. Problem you will have is that the rs232 port of the Amiga can only be set to 100 baud (bits per sec. probably this time) as the LOWEST speed! (It one of the little things the Amiga designers forgot :=) ) If you use a 75/1200 modem with an interspeeder the modem would take care of the speed conversion. However those modems are much more expensive. > >Altzo, is it possible to transmit 75 bit/s and receive 1200 bit/s over >the serial port? At the same time? > > wonders kitte d5kwedb@dtek.chalmers.se usualy in such cases (software) switching has to be done when changing from receiving to sending and vice versa. +-----------------------------------------------------------------+ | The smoker you drink,| Gert Kanis, SWP | | the W.C. | Nixdorf Computer BV, Postbus 29 | |----------------------| 4130 EA Vianen, Netherlands. | | I do not represent | E-mail : targon!gert@nluug.nl | | anyone elses opinion.| or ..!mcvax!targon!gert | +-----------------------------------------------------------------+
ckp@grebyn.com (Checkpoint Technologies) (07/15/89)
In article <539@vice2utc.chalmers.se> d5kwedb@hacke9.dtek.chalmers.se (Kristian Wedberg) writes: >I've written a Videotex program (Prestel type) for the Amiga, a kind of >communication program. Trouble is, here in Sweden some folks have 75/1200 >modems instead of the more normal 1200/1200. > >As it is, I have no idea how to support 75/1200, or indeed, if it's at all >possible. > >Altzo, is it possible to transmit 75 bit/s and receive 1200 bit/s over >the serial port? At the same time? Or would you need some kind of transformer? > First of all, the Amiga's serial port bottoms out at 112 baud. It's not possible to run it any slower. Secondly, the Amiga serial port does not allow split baud rates, that is, running transmit and receive at different speeds. The serial chip we use on our dual port serial card allows both the 75 baud speed, and split rate operation, though the driver we've written does not support split baud rates; and it plugs into a Zorro slot, and I imagine you're really talking about the A500. It's not possible to bang the bits on the Amiga serial port manually, so I don't know how to solve your problem, sorry. -- First comes the logo: C H E C K P O I N T T E C H N O L O G I E S / / \\ / / Then, the disclaimer: All expressed opinions are, indeed, factual. \ / o Now for the witty part: I'm pink, therefore, I'm spam! \/
marten@kuling.UUCP (M}rten Norman) (07/16/89)
From article <539@vice2utc.chalmers.se>, by d5kwedb@hacke9.dtek.chalmers.se. (Kristian Wedberg): > > Altzo, is it possible to transmit 75 bit/s and receive 1200 bit/s over > the serial port? At the same time? Or would you need some kind of transformer? As 1200/75=16 it _should_ be possible, if you are willing to fiddle with the hardware registers. Just send 16 "1200-speed-bits" to represent a "75-bit". The Hardware serial output register should agree with this, but i _dont_ think it's supported in standard software :-) --- M}rten Norman EMAIL: marten@kuling.uucp
jms@tardis.Tymnet.COM (Joe Smith) (07/18/89)
In article <1052@kuling.UUCP> marten@kuling.UUCP (M}rten Norman) writes: >As 1200/75=16 it _should_ be possible, if you are willing to fiddle with the >hardware registers. Just send 16 "1200-speed-bits" to represent a "75-bit". >The Hardware serial output register should agree with this, but i _dont_ >think it's supported in standard software :-) When you send 8 bits to an async line, the hardware sends 10 bits by adding a start bit and a stop bit. Although one byte at 75 baud takes the same amount of time to transmit as 16 bytes at 1200 baud (160 bit times total), you can only specify 128 of the 160 bits. The remaining 32 bits will screw up the receiver at the far end. -- Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@tymix.tymnet.com McDonnell Douglas FSCO | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-D21 | PDP-10 support: My car's license plate is "POPJ P," San Jose, CA 95161-9019 | narrator.device: "I didn't say that, my Amiga did!"
rouaix@inria.inria.fr (Francois Rouaix) (07/18/89)
[.... deleted everything about talking to a 75/1200 modem with software hacks] These 75/1200 modems are used for Videotex. you talk to them from the serial port AT 1200 bauds ! I'm running a BBS with of these modems, I use one of these also on my 'work' amiga. For the french videotex (I assume it is the same everywhere...) configuring the serial port is quite simple : 1200bauds, 7bits(r/w), even. --Francois -- *- Francois Rouaix // We are all prisoners here, * *- rouaix@inria.inria.fr \X/ of our own device * *- SYSOP of Sgt. Flam's Lonely Amigas Club. (33) (1) 39-55-84-59 (Videotext) * Disclaimer: Opinions expressed are my own, not those of my employer.
marten@kuling.UUCP (M}rten Norman) (07/25/89)
From article <431@tardis.Tymnet.COM>, by jms@tardis.Tymnet.COM (Joe Smith): > In article <1052@kuling.UUCP> marten@kuling.UUCP (M}rten Norman) writes: >>As 1200/75=16 it _should_ be possible, if you are willing to fiddle with the >>hardware registers. Just send 16 "1200-speed-bits" to represent a "75-bit". >>The Hardware serial output register should agree with this, but i _dont_ >>think it's supported in standard software :-) > > When you send 8 bits to an async line, the hardware sends 10 bits by > adding a start bit and a stop bit. Although one byte at 75 baud takes > the same amount of time to transmit as 16 bytes at 1200 baud (160 bit times > total), you can only specify 128 of the 160 bits. The remaining 32 bits > will screw up the receiver at the far end. > You are _so_ right! I overlooked the START/STOP-bit "feature"... Think I _should_ have done a double-check _before_ I launched some fake hope :-) --- M}rten Norman Email:marten@kuling.UUCP
doug@xdos.UUCP (Doug Merritt) (08/15/89)
In article <431@tardis.Tymnet.COM> jms@tardis.Tymnet.COM (Joe Smith) writes: >In article <1052@kuling.UUCP> marten@kuling.UUCP (M}rten Norman) writes: >When you send 8 bits to an async line, the hardware sends 10 bits by >adding a start bit and a stop bit. Although one byte at 75 baud takes >the same amount of time to transmit as 16 bytes at 1200 baud (160 bit times >total), you can only specify 128 of the 160 bits. The remaining 32 bits >will screw up the receiver at the far end. I would think there's a chance that they wouldn't screw it up, since we're basically talking about what would look like a glitch in 1/16th of the received waveform. Would depend on how the receiver hardware was designed, wouldn't it? Might still be worth a try. Doug -- Doug Merritt {pyramid,apple}!xdos!doug Member, Crusaders for a Better Tomorrow Professional Wildeyed Visionary
ecarroll@csvax1.cs.tcd.ie (Eddy Carroll) (08/28/89)
In article <431@xdos.UUCP>, doug@xdos.UUCP (Doug Merritt) writes: > In article <431@tardis.Tymnet.COM> jms@tardis.Tymnet.COM (Joe Smith) writes: >>In article <1052@kuling.UUCP> marten@kuling.UUCP (M}rten Norman) writes: >>When you send 8 bits to an async line, the hardware sends 10 bits by >>adding a start bit and a stop bit. Although one byte at 75 baud takes >>the same amount of time to transmit as 16 bytes at 1200 baud (160 bit times >>total), you can only specify 128 of the 160 bits. The remaining 32 bits >>will screw up the receiver at the far end. > > I would think there's a chance that they wouldn't screw it up, since > we're basically talking about what would look like a glitch in 1/16th > of the received waveform. Would depend on how the receiver hardware was > designed, wouldn't it? Might still be worth a try. > Doug I posted a message a while ago in comp.sys.amiga.tech about this, but some folks may have missed it. In fact, the method outlined above works pretty well, and it formed the basis of a modem driver I wrote for use with Compunet (a UK 1200/75-based service). A little tweaking of the output signal away from what might look like the optimum can help quite a lot in fooling the receiver that you are sending at 75 baud when you're really sending at 1200 baud. Anyway, I have a document I did up which explains the whole thing in more detail, gives example C code etc. If anyone wants a copy, send me email to the address below. Eddy Carroll ecarroll@vax1.tcd.ie