Maxim Integrated Teridian V.22 bis Linux Softmodem for 73M1822/73M1922 MicroDAA - Manual (Page 61)

UG_1x22_043 V.22 bis Linux Softmodem for 73M1x22 MicroDAA User Guide
Rev. 1.5 61
V23 Operation
In addition to the standard V23 recommendation, the TSC Softmodem also adds a special
feature referred to as V23 PAVI operation. This feature implements the mechanism to
allow the swapping or turn-around of the transmission channels during communications.
Transmission speed may then be monitored dynamically during a connection; the
transmitter at 75 bps may become the transmitter at 1200 bps, and vice versa.
The process of switching from transmission at 75 bps to 1200 bps is referred as Back to
Main Channel Turnaround.
The process of switching from transmission at 1200 bps to 75 bps is referred as Main to
Back Channel Turnaround.
V23 PAVI operation includes also a Teletel option that is characterized by the transmission
of some special characters during communications.
The mechanism of this operation is described in the following document:
“Spécifications Techniques d’Utilisation du Minitel 1B” - Edition of Nov 1986 -
Edited by :
Ministère des Postes et des Télécommunications
Direction Générale des Télécommunications
Direction des Affaires Commerciales et Télématiques
If you are interested by further details on the V23 operation in the TSC Softmodem, please
request the related application note entitled “73M2901_V23_Operation” from your local
TERIDIAN’s representative.
Line in Use/Parallel Pick Up Detection Support
A modem may share the phone line with other equipment such as telephone sets or
emergency equipment (alarms, etc) and may be programmed to place a call without
notifying the customer. Some standards require that the unattended modem have low
priority on the line. Therefore the modem should not be allowed to seize the line if the line
is in use by any other equipment and should release the line as soon as any other
equipment tries to place a call. The TSC Softmodem supports two methods of detecting
Line-In-Use; by looking at the battery voltage from the central office and by detecting
energy on the line from other devices or voice, before going off hook. The TSC
Softmodem also detects another device going off hook in parallel with the modem by
sensing the drop in voltage caused by the parallel device. When these features are active
the modem will immediately relinquish the line to the other device and send a message to
the host informing it of the event or condition (LIU-V, LIU-E, PPU-E or PPU-V).
The Line-in-Use/Parallel Pick-up feature of the TSC Softmodem provides the designer
support for these features with only a minimum of additional hardware.
If you are interested by further details on the Line In Use/Parallel Pick-up detection support
in the TSC Softmodem, please request the related application note entitled
“73M2901CL_AN_LIU-PPU_Rx.x” from your local TERIDIAN representative.