Envoy ACP/XF Application Programming Manual

Features Common to Bit-Synchronous Protocols
EnvoyACP/XF Application Programming Manual–132179
B-10
Mode-Setting Commands
EnvoyACP/XF formats some U-frame commands as a result of procedure calls; in other
cases, you must format the command by specifying the appropriate value in the first byte
of the message control word (MCW). Additional information on the MCW is provided
with the READ, WRITE, and WRITEREAD procedure call descriptions in Section 4,
System Procedure Call Specifics for EnvoyACP/XF.
Mode-Setting Commands
To establish or change the mode of the addressed, secondary/combined station, the
primary/combined station transmits a U-frame, including a mode-setting command. A
secondary station remains in the established mode until it receives another mode-setting
command. A combined station remains in the established mode until the station receives
another mode-setting command or until the station transmits a mode-setting command
that is acknowledged by the remote station.
Your application directs EnvoyACP/XF to transmit these mode-setting commands by
issuing CONTROL or SETMODE procedure calls. The procedure calls are summarized
in Section 4, System Procedure Call Specifics for EnvoyACP/XF
. Protocol-specific
information is provided in Sections 2 through 4.
Information Transfer Commands
The primary/combined station transmits a U-frame that includes one of the following
commands to communicate information relating to the communication process.
UI Command
The Unnumbered Information (UI) command transfers an information field to a
secondary/combined station or groups of secondary stations without affecting the
number sent (Ns) and number received (Nr) variables. An information field may be
present. UI frame information concerns higher-level status, operation interruption,
time-of-day notification, or link-initialization parameters. For example, EnvoyACP/XF
uses the UI frame to establish a call with the V.25 bis automatic-calling procedure (see
Automatic Calling for V.25 bis Modems
on page 1-13).
Your application directs EnvoyACP/XF to transmit a UI command by using a WRITE or
WRITEREAD procedure call to place the appropriate value in the first byte of the
MCW.
UP Command
The Unnumbered Poll (UP) command solicits response frames from a single
secondary/combined station or from a group of secondary stations.
Your application directs EnvoyACP/XF to transmit a UP command by using a WRITE or
WRITEREAD procedure call to place the appropriate value in the first byte of the
MCW.