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V.25 bis Dialer Operation
DTE INTERFACE PINS
DTR Pin Operation
DCD Pin Operation
6-2
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.
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.
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.
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.
UTA220/UTA220k
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