ZyXEL Elite 2864 User Guide - Page 129

Chapter 11 SYNCHRONOUS OPERATION This chapter introduces you to the use of the 2864 series modem for synchronous operation. 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 synchronous. 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 asynchronous 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 generated 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. + INTERNAL EXTERNAL SLAVE AT&X0 AT&X1 AT&X2 The modem provides the clock and sends it to the DTE. Adaptive rate can be used. (Default) The DTE provides the clock and sends it to the modem. Must use auto-retrain, cannot use adaptive rate. Recovered receiver clock serves as transmission clock. 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. + IGNORED AT&R1 CTS TRACKS AT&R0 RTS RTS is ignored; always assumed to be ON. (Default) Delay before CTS responds to RTS's change. The delay is set in the S26 register. 11-1