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RS-232 Signals
This section describes each of the signals supported on the modem’s RS-232 socket.
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Pin assignments are only applicable to products with a 25-pin DB-25 connector.
Refer to your Product Guide for information regarding the pin assignments for
your product.
Transmit Data (TxD) - Pin 2
The computer transmits data to the modem via this pin.
Receive Data (RxD) - Pin 3
The computer receives data from the modem via this pin.
Request To Send (RTS) - Pin 4
This signal indicates to the modem whether the computer is ready to begin sending data to it.
When RTS/CTS flow control is enabled, the RTS signal is used by the computer to pause the
transmission of data from the modem to it. If RTS/ CTS flow control is not selected, the RTS
signal is ignored when the modem is in asynchronous mode or local command state.
Clear To Send (CTS) - Pin 5
This signal indicates to the computer the modem is ready to begin receiving data from it. When
RTS/CTS flow control is enabled, the CTS signal is used by the modem to pause the
transmission of data from the computer to it. If RTS/CTS flow control is not selected CTS will
always be asserted when asynchronous operation is selected. With synchronous mode selected
CTS will be lowered when the modem is on line until such time as DSR and DCD are asserted.
CTS will always be asserted in local command state.
Data Set Ready (DSR) - Pin 6
This signal indicates to the computer that the modem is ready to begin communications.
In asynchronous mode, this signal will be asserted whenever the modem is switched on and is
not performing a test. In synchronous mode, the DSR will only be asserted when the modem is
off hook.
The &S command lets you control the state of the DSR signal.
Signal Ground (SG) - Pin 7
Ground for all signals on the RS-232 socket.