Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 81)

AN93
Rev. 1.3 81
%V2
Automatic Line Status Detection - Adaptive Method.
Description: Before going off-hook with the ATD, ATO, or ATA commands, the ISOmodem compares
the line voltage (via LVCS) to the NLIU (U85) register:
Loop Voltage
Action
0
 LVCS  (0.0625 x NLIU)
Report NO LINE and remain on-hook.
(0.0625 x NLIU) < LVCS
 (0.85 x NLIU) Report LINE IN USE and remain on-hook.
(0.85 x NLIU) < LCVS Go off-hook and establish a modem connection.
The NLIU register is updated every 1 ms with the minimum non-zero value of LVCS in the last
30 ms. This allows the ISOmodem to eliminate errors due to 50/60 Hz interference and also adapt
to relatively slow changes in the on-hook dc reference value on the telephone line. This algorithm
does not allow any non-zero values for NLIU below 0x0007. The host may also initialize NLIU prior
to issuing the %V2 command. Once the call has begun, the off-hook intrusion algorithm (described
in "6.6.2. Off-Hook Condition" on page 162) operates normally. In addition, the ISOmodem reports
NO LINE if the telephone line is completely disconnected. If the HOI (U77, bit 11) bit is set, LINE IN
USE is reported upon intrusion.
Table 42. Extended AT\ Command Set
Command Action
\$ Display AT\ command settings (see text for details).
\Bn Character length is automatically set in autobaud mode.
\B0 Reserved
\B1 7N1—Seven data bits, no parity, one stop bit, one start bit, nine bits total (\N0 only)
\B2 7P1—Seven data bits, parity optioned by \P, one stop bit, one start bit, ten bits total
\B3 8N1—Eight data bits, no parity, one stop bit, one start bit, 10 bits total (default)
\B5
8P1—Eight data bits, parity optioned by \P, one stop bit, one start bit, 11 bits total (\N0 only) This
mode is not allowed with a parallel or SPI interface.
\B6
8X1—Eight data bits, one escape bit, one stop bit, one start bit, 11 bits total (enables ninth-bit
escape mode) This mode is not allowed with a parallel or SPI interface.
\Nn Asynchronous protocol.
\N0 Wire mode (no error correction, no compression).
Notes:
1. When in autobaud mode, \B0, \B1, and \P1 is not detected automatically. The combination of \B2 and \P3 is detected.
This is compatible with seven data bits, no parity, two stop bits. Seven data bits, no parity, one stop bit may be forced by
sending AT\T17\B1.
2. After changing the baud rate, the result code OK is sent at the old DTE rate. Subsequent commands must be sent at
the new rate. If the ISOmodem is configured in autobaud mode, AT commands \T0 through \T15 lock the new baud rate
and disable autobaud. To eliminate any possibility of a race condition between the receipt of the result code and the
changing of the UART speed, CTS is de-asserted while the result code is being sent until after the rate has been
successfully changed. The host should send the \T command and wait for the OK response. After OK has been
received, the host may send data at the new rate as soon as CTS is asserted. The \T command should be the last
command sent in a multi-command line and may not be used on the same command line as :U or :R commands. If it is
not, the OK from the \T command is sent at the old DTE rate, and other result codes are sent at the new DTE rate.
3. The autobaud feature does not detect this rate.
4. Default is \T16 if autobaud is selected by reset-strap option; otherwise default is \T9 (19.2 kbps).
Table 41. Extended AT% Command Set (Continued)