Msg: 7306 *Conference*

11-07-97 03:16:01

From: COMET _

To : PETER VOLLAN

Subj: REPLY TO MSG #7263 (MODEM)

The MC14412 (modem) chip is wired in the Model 100 to be optimized for 0-300bps
operation, since pins 6 (Rx rate) and 14 (Type) have a high input.  If you
rewired pin 6 to low input (ground), then the modem chip will be optimized for
0-600bps operation.  [pp 117-118 of TRS-80 Model 100 Technical Reference
Manual, Radio Shack cat. no. 26-3810].
 
The modem doesn't control the actual baud rate used; it is a "dumb" modem.  The
rate at which the computer feeds it data is the rate that is actually used--so
if you send it data at twice the speed, it will transmit at 600 bps.  The
reason you cannot keep raising the speed beyond this is that the various modem
speeds have different standards.
 
Frequency Shift Keying, or "Bell 103", assigns frequencies for both computers
to have a "high" and "low" tone.  The practical limit for this protocol is
about 600 bps.