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11–1
Chapter 11
SYNCHRONOUS OPERATION
This chapter introduces you to the use of the 2864 series modem for synchronous oper-
ation. Use the modem as a synchronous modem when it is connected to a synchronous
computer or terminal. Be sure that the remote modem and system are also set to syn-
chronous. Synchronous operation applies to all of the non-FSK modes the modem is
supplied with.
The serial port models support synchronous mode operation. The internal card
model has a built-in PC asynchronous serial port and can only be used in asynchro-
nous mode. The parallel port interface supports asynchronous mode only.
Before synchronous transfers are started, some initial settings should be made.
Clock Options
Synchronous data must be transmitted and received with a common timing clock. This
timing clock is used to transmit data from the DTE to the modem which modulates the
data according to this clock. The receiving modem recovers the clock and data from the
carrier and sends the data to the receiving DTE along with the clock. There are three
types of transmission synchronous clock sources to choose from. The internal clock is the
one that suits most applications and is the default; in this case, the clock signal is generat-
ed by the sending modem. The slave clock is used when in remote digital loopback
mode. The external clock is a signal generated by the sending DTE.
RTS Options
There are two RTS options. The choice depends on application and host/terminal
requirements. In asynchronous mode RTS is used as a hardware flow control signal.
+ INTERNAL AT&X0 The modem provides the clock and sends it to
the DTE. Adaptive rate can be used. (Default)
EXTERNAL AT&X1 The DTE provides the clock and sends it to the
modem. Must use auto-retrain, cannot use
adaptive rate.
SLAVE AT&X2 Recovered receiver clock serves as transmis-
sion clock.
+ IGNORED AT&R1 RTS is ignored; always assumed to be ON.
(Default)
CTS TRACKS
RTS
AT&R0 Delay before CTS responds to RTS's change.
The delay is set in the S26 register.