Northern UTA220/UTA220k manual DTE Interface Pins, DTR Pin Operation, DCD Pin Operation

V.25 bis Dialer Operation

In HDLC operation mode, V.25 bis command and response messages are contained in standard HDLC Unnumbered Information (UI) frames (Figure 6-1). Each field consists of one or more eight bit octets. The eighth bit (parity bit) of each octet in the Message field is ignored by the UTA220.

Figure 6-1. HDLC Frame for V.25 bis Messages

In BISYNC mode of operation, all V.25 bis commands and response messages are contained in frames (Figure 6-2).

Figure 6-2. BISYNC Frame for V.25 bis Messages

The message field in the frame is composed of 7-bit IA5 characters with the eighth bit set for odd parity. If the HDLC or BISYNC frames are improperly formatted, the frames are ignored.

For more information on V.25 bis formatting and protocol procedures, refer to the CCITT V.25 bis recommendation.

DTE INTERFACE PINS

The UTA220 supports V.35 and EIA-232 interfaces to the DTE for V.25 bis dialing. The function of some pins on the EIA-232 interface is different than in other synchronous modes.

DTR Pin Operation

For the UTA220 to accept V.25 bis commands, the DTE must hold the DTR signal high. When configured for V.25 bis dialing, the DTR pin option setting does not apply because the V.25 bis specification explicitly defines how the dialer will respond to changes in DTR.

DCD Pin Operation

The default operation of the V.25 bis dialer asserts the DCD pin when DTR is high (DCD follows DTR). Some devices may require DCD to be low until the connection is established. For those devices, the UTA220 can be configured to only raise DCD upon connection by setting the DCD pin option to NORMAL. The DCD pin option setting of ON is the default for CCITT V.25 bis operation.

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