SI2493-C-GT Silicon Laboratories Inc, SI2493-C-GT Datasheet - Page 54

• Manufacturer Part Number: SI2493-C-GT
• Description: IC ISOMODEM SYSTEM-SIDE 24TSSOP
• Manufacturer: Silicon Laboratories Inc

Specifications of SI2493-C-GT

• Mfg Application Notes: SI2493/57/34/15/04, Appl Note AN93
• Data Format: V.21, V.22, V.23, V.29, V.32, V.34, V.90, V.92, Bell 103, Bell 212A
• Baud Rates: 56k
• Interface: Parallel
• Voltage - Supply: 3 V ~ 3.6 V
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AN93
3.1.10. Escape Methods
There are four ways to escape from data mode and
return to command mode once a connection is
established. Three of these, “+++”, “9th Bit”, and the
“Escape Pin”, allow the connection to be maintained
while one or both modems are in the command mode.
These three escape methods can be concurrently
enabled, and any enabled escape method functions.
For example, if “+++” and the “Escape Pin” are both
enabled, either returns the modem to the command
mode from the data mode. The fourth escape method is
to terminate the connection.
Always wait for the “OK” before entering the next
command after an escape. When making a new
connection, do not try to escape between the connect
message and the protocol message. An escape attempt
in this interval may fail because the modem is not in
data mode until after the protocol message.
3.1.10.1. “+++” Escape
The “+++” escape is enabled by default and is
controlled by U70[13] (TES). There are equal guard
time periods before (leading) and after (trailing) the
“+++” set by the S-Register, S12, during which there
must be no UART activity. If this UART inactivity
criterion is met, the Si2493/57/34/15/04 escapes to the
command mode at the end of the S12 time period
following the “+++”. Any activity in the UART during
either the leading or trailing time period causes the
ISOmodem to ignore the escape request and remain in
data mode. Timing for this escape sequence is
illustrated in Figure 11.
54
Guard Tim e = S12 (20 m sec units)
Default Guard Tim e S12 = 50 (1.0 sec)
Guard Tim e Range = 10–255 (0.2–5.1 sec)
Leading Guard
Figure 11. “+++” Escape Timing
Tim e
+++
Trailing Guard
Tim e
Rev. 0.9
3.1.10.2. “9th Bit” Escape
The “9th Bit” escape mode feature is enabled by
sending the AT\B6 command through autobaud, which
detects a 9th bit space as “9th bit” escape mode. If this
escape method is selected, a 1 detected on the ninth bit
in a data word returns the modem to the command
mode. The 9th bit is ignored when the modem is in the
command mode. Timing for this escape sequence is
illustrated in Figure 12.
3.1.10.3. “Escape Pin” Escape
The “Escape Pin” is controlled by U70[15] (HES). This
bit is 0 by default, which disables the Escape pin, ESC,
(Si2493/57/34/15/04, pin 22). If HES is set to a 1, a high
level on Si2493/57/34/15/04, pin 22, causes the modem
to transition to the on-line command mode. The ESC pin
status is polled by the processor, and there is a latency
before the “OK” is received and the modem is in
command mode. Keep the “escape pin” active until the
“OK” is received. In parallel interface mode, the function
of the Escape pin is replaced by bit 2 in the Parallel
Interface Register 1. Setting bit 2 to a 1 causes the
modem to escape to the command mode.
While in data mode, an escape to command mode
occurs if ESC is sampled as negated for at least 60 ms,
then sampled asserted for at least 60 ms. The modem
is then prepared to accept AT commands, regardless of
whether the “OK” has been sent to the host. If the
modem is already in command mode, the modem does
not send the “OK”.
In practice, it is difficult to determine the exact boundary
between command mode and data mode. Time the
ESC 100 ms low and 100 ms high, and expect that the
modem has transitioned to command mode. Then,
dump the receive buffer after 100 ms, send “AT”, and
wait for “OK”. This way, you know the modem is in
command mode because the “OK” is caused by the
“AT” and not by the ESC toggling.