Specifications

Si2493
36 Rev. 1.3
%V2 Automatic Line Status Detection—Adaptive Method.
Description: Before going off-hook with the ATD, ATO, or ATA commands, the Si2493 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 Si2493 to eliminate errors due to 50/60 Hz interference and also adapt to rel-
atively slow change 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 "4.15.2.
Off-Hook Intrusion Detection" on page 20) operates normally. In addition, the Si2493 will report “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 10. Extended AT% Command Set (Command Defaults in Bold) (Continued)
Command Action