Specifications

AN93
Rev. 0.8 43
%V2 Automatic Line Status Detection - Adaptive Method.
Description: Before going off-hook with the ATD, ATO, or ATA commands, the Si2493/57/34/15/04
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 Si2493/57/34/15/04 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 algo-
rithm 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 "Intrusion Detection—Off-Hook Condition" on page 147) operates normally. In addi-
tion, the Si2493/57/34/15/04 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 22. Extended AT% Command Set (Continued)