Cisco Systems C819GUK9, C819HG4GVK9 manual Configuring Low-Speed Serial Interfaces

Chapter 8 Configuring the Serial Interface

How to Configure Serial Interfaces

Configuring Low-Speed Serial Interfaces

This section describes how to configure low-speed serial interfaces and contains the following sections:

•Understanding Half-Duplex DTE and DCE State Machines, page 8-14

•Changing Between Synchronous and Asynchronous Modes, page 8-18

For configuration examples, see the “Low-Speed Serial Interface: Examples” section on page 8-20.

Understanding Half-Duplex DTE and DCE State Machines

The following sections describe the communication between half-duplex DTE transmit and receive state machines and half-duplex DCE transmit and receive state machines.

Half-Duplex DTE State Machines

As shown in Figure 3, the half-duplex DTE transmit state machine for low-speed interfaces remains in the ready state when it is quiescent. When a frame is available for transmission, the state machine enters the transmit delay state and waits for a time period, which is defined by the half-duplex timer transmit-delaycommand. The default is 0 milliseconds. Transmission delays are used for debugging half-duplex links and assisting lower-speed receivers that cannot process back-to-back frames.

Figure 3 Half-Duplex DTE Transmit State Machine

After idling for a defined number of milliseconds (ms), the state machine asserts a request to send (RTS) signal and changes to the wait-clear-to-send (CTS) state for the DCE to assert CTS. A timeout timer with a value set by the half-duplex timer rts-timeoutcommand starts. The default is 3 ms. If the timeout timer expires before CTS is asserted, the state machine returns to the ready state and deasserts RTS. If CTS is asserted before the timer expires, the state machine enters the transmit state and sends the frames.

	Cisco 819 Series Integrated Services Routers Software Configuration Guide
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