6.19
SNM15
V.25 bis
Digicom SpA
Synchronous V.25bis commands and indications
In synchronous V.25bis, in order to send commands to the
modem, the frame structure must follow V.25bis reccomandation
concerning the use of a bit oriented protocol (HDLC)
The frame structure is as following:
F A C MESSAGE FCS F
F
(Flag start/end frame) It is a fixed and standard
field of bit oriented protocols (HDLC/SDLC)
and it corresponds to 7E in hexadecimal or to
01111110 in bynary.
A
(Address) This is usually a changing field but in
this case it has a fixed value and it must be FF
(hex) or 11111111 (binary).
C
(Control) This is usually a changing field but in
this case it has a fixed value and it must be 13
(hex) or 11001000 (binary).
FCS
This is a changing field which depends on the
frame content for error correction.
MESSAGE
Changing field containing the message
according to V.25bis command set.
The format of characters, included in “message” field, must use
IA5 alphabet (ASCII) with 7 bit data and ODD parity.