if you want a modem chip you can use the National Semiconductor 74VHC943 or 942 they are 300 bps modems chips and still avalable from Jameco Electronics. Felix Centeno centella@telcel.net.ve http://www.geocities.com/CapeCanaveral/Hangar/2372/ -----Original Message----- From: Chris Eddy To: PICLIST@MITVMA.MIT.EDU Date: Martes 16 de Diciembre de 1997 10:59 PM Subject: Re: PIC to modem >Ernesto: > >Just a word of warning about the TCM3105. It was discontinued last year by TI >with no alternate source. If you have found a second source, I would love to >hear of it. As it is, I designed a TDK(Silicon Systems) V.21 part in in its >place. > >By the way, the reason that I find the old V.21 is so useful is that you can > half >duplex it, as it does not actually come up and train into service. You can >handshake the carrier on and off as often as you like. It also has a somewhat >fixed delay in it, whereas many of the higher speed 'modern' modems will queue > up >a chunk of data. V.21 comes in handy for short haul sensor data and the like. > >I don't have a catalog handy, but Multi-tech in the US have some of the older >designs in production, and may have your V21. I am fairly certain that they > make >a bell202. > >There ain't many offerings in the old 1200 bps area, though, and if anyone knows >of other bell 202 or V.21 products, I would love to hear of it. > >Chris Eddy >Pioneer Microsystems, Inc. > >Ernesto Tolocka wrote: > >> Hi Piclisters! >> >> I'm using a TCM3105 single chip modem to send data trhu the cellular network, >> from a PIC16c65 mounted on a car to a PC. The data flow is "half-duplex", >> only from the PIC. This chip uses FSK modulation (V21) and I tested it when >> the transmitter is >> moving and works fine, but is expensive and need a "custom" modem in the PC, >> since >> i cant found a modem card supporting V21. >> Some people tell me that V22 and other modem standards that uses PSK or QAM >> modulation >> techniques are not useful in mobile applications. Is this correct? >> Can I use a V22 chip? >> >> Regards, >> Ernesto Tolocka >> etolocka@onenet.com.ar >> Argentina >