Ascotel IntelliGate 2025/2045/2065
Part 4 Cabling interfaces 789
The DCD signal should only be used if a DCE is connected with a DTE.
DCD is activated by the DCE once the connection to the DTE is established.
Flow control
Depending on the set mode, the data flow is controlled differently by the equip-
ment involved. The most common modes are Xon / Xoff or RTS /CTS.
Xon / Xoff mode
This mode is also known as a software handshake.
The data flow is controlled by the data receiving equipment. The data receiving
equipment sends an SW signal over the data line as soon as its input memory is
full, and an SW signal as soon as it is ready to receive again.
Xon / Xoff requires only a three-wire connection for signals RxD, TxD and SGND.
Drawback: The data transmitting equipment cannot tell whether or not a receiv-
ing equipment is connected.
RTS / CTS mode
This mode is also known as a hardware handshake.
The two equipment involved use the RTS and CTS signals to indicate that they are
ready to send and to receive, each signal being transmitted over a separate sig-
nalling line.
Advantage: Data exchange cannot take place if there is no equipment ready to
receive. For example no more data will be sent to the printer if the printer is
switched off or out of paper.
Note:
To exclude any transmission errors, always operate the printer on the
PBX in RTS / CTS mode.
Initialization values
Tab. 4.47: V.24 initialization values
Interface Transmission rate (bit/s) Format Parity Stop bit Flow control
COM1 9600 8 bit none 1 HW
COM2 115 200 8 bit none 1 HW
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