wwg2101@venus.tamu.edu (GILPIN, WESLEY WILSON) (02/22/91)
Could someone please tell me how to implement a carrier detect routine for use with the modem port? What I want is a boolean function returning true if the modem is currently detecting a carrier signal, and I can't for the life of me figure out how to read the CD line from the modem. I am working in pascal on an SE, but I undertstand C, so example code in C or Pascal would be fine. Wes WWG2101@TAMVENUS
russotto@eng.umd.edu (Matthew T. Russotto) (02/22/91)
In article <12468@helios.TAMU.EDU> wwg2101@venus.tamu.edu writes: >Could someone please tell me how to implement a carrier detect routine for >use with the modem port? What I want is a boolean function returning true if >the modem is currently detecting a carrier signal, and I can't for the life >of me figure out how to read the CD line from the modem. I am working in >pascal on an SE, but I undertstand C, so example code in C or Pascal would >be fine. Most cables for the Mac do not support the carrier detect line-- they either support DTR/DSR or CTS/RTS. On some modems, DSR and CD are equivalent, so you can read the status of CTS to see if you have a carrier. On others, you can make a custom cable and connect CD (pin 8 on the DCE) to pin 7 on the Mac. In either case, reading the status of these lines is going to require some assembly language, and a look at the manual for the serial chip, unless the Comm Toolbox has added this ability. -- Matthew T. Russotto russotto@eng.umd.edu russotto@wam.umd.edu .sig under construction, like the rest of this campus.
jackb@MDI.COM (Jack Brindle) (02/23/91)
In article <1991Feb22.151625.26340@eng.umd.edu> russotto@eng.umd.edu (Matthew T. Russotto) writes: > >Most cables for the Mac do not support the carrier detect line-- they either >support DTR/DSR or CTS/RTS. On some modems, DSR and CD are equivalent, so >you can read the status of CTS to see if you have a carrier. On >others, you can make a custom cable and connect CD (pin 8 on the DCE) to >pin 7 on the Mac. In either case, reading the status of these lines >is going to require some assembly language, and a look at the manual for >the serial chip, unless the Comm Toolbox has added this ability. > >-- >Matthew T. Russotto russotto@eng.umd.edu russotto@wam.umd.edu > .sig under construction, like the rest of this campus. Actually, the exact opposite is true, at least for Apple cables. Apple's cables have always brought the DCD line (pin8) into the Mac's HSK input line, a very useless configuration in most cases. Since most of my packet radio applications talk to boxes that require handshaking, I have to tell customers to use a cable that configures the cts output into the Mac's HSK input. By the way, in the Apple configuration, the result is unusable, since the CD line is negated by the packet TNC until someone connects. Thus you can't even set the modem up unless you ignore the HSK input signal! Secondly, the Mac's serial driver's have supported notification from the driver of a change in the state of the HSKin line ever since the original loose leaf Inside Mac days. Take a good look at the serial driver chapter in Inside Mac Volume II. It works quite nicely, and does not require directly programming the SCC. The state of the input pins (HSKin and GPi) is also available, although configuring the GPi is in itself a pain. Look at Volume 5 of I.M. for info on using that pin. Also, the serial driver is discussed in volume 4 for other "features" that were added. This means you need to look at Vol 2, 4 and 5. Hope you already have them (or have a fat wallet :-)... ). Jack Brindle WA4FIB mdisea!MDI.COM!jackb