Z02215
Single Chip Modem with Integrated Controller, Data Pump, and AFE
44
Minitel Line Reversal
The modem contains code that supports the Minitel Line Reversal method, as
specified in the STUM documentation (Minitel specification). Table 8 describes the
terminology and definitions used in this section.
Table 8. Minitel Terminology and Definitions
STATIC REVERSE mode
DYNAMIC REVERSE mode
MASTER mode
SLAVE mode
Direct turnaround
Reverse turnaround
The ability of the modem to dial and connect in REVERSE
mode (Rx@75 bps, Tx @ 1200 bps).
The ability of the modem to enter REVERSE mode one
connected (switching from one mode to the next).
NORMAL mode (Tx75/Rx1200 from the originator side)
REVERSE mode (Tx1200/Rx75 from the originator side)
Entering REVERSE mode
Entering NORMAL mode
General Description of the Turnaround Principle
Only the modem which is in MASTER mode can physically initiate a turnaround by
changing its carrier from 390 Hz to 1300 Hz. When this change occurs the remote
modem, which is in SLAVE mode, detects the changing carrier and also reverses.
The Minitel STUM specifies character sequences that are exchanged by the Data
Terminal Equipment and the PAVI (Videotex server) to determine if the PAVI can
reverse (before the first turnaround). Some character sequences are also sent
through the Minitel modem to request a Reverse turnaround from the PAVI, and
then acknowledge the turnaround. The modem ignores these sequences.
DYNAMIC REVERSE Mode
Direct Turnaround
To perform a direct turnaround, the user enters into ON-LINE COMMAND mode
by sending the
+++
escape command or by making an active/inactive DTR transi-
tion (if
AT
and
DI
has been previously executed). The user then sends the
ATRO
command (an
R
command followed by an
O
command). As the modem supports
the Time Independent Escape Sequence (
TIES),
the following command may be
sent.
+++ATRO<CR>
The modem then goes off-line, executes the
R
command, and returns ON-LINE.
PS001907-0904
Minitel Line Reversal
ZILOG [ ZILOG, INC. ]
