Specifications

Si2457/Si2434/Si2415
Rev. 0.91 31
%V1 Automatic Line Status Detection—Fixed Method.
Description: Before going off-hook with the ATD, ATO, or ATA commands, the Si2457/34/15 com-
pares the line voltage (via LVCS) to registers NOLN (U83) and LIUS (U84):
Loop Voltage
Action
0 ≤ LVCS ≤ NOLN Report “NO LINE” and remain on-hook.
NOLN ≤ LVCS ≤ LIUS Report “LINE IN USE” and remain on-hook.
LIUS ≤ LCVS Go off-hook and establish a modem connection.
Once the call has begun, the off-hook intrusion algorithm (described in "Off-Hook Intrusion Detec-
tion" on page 18) operates normally. In addition, the Si2457/34/15 will report “NO LINE” if the tele-
phone line is completely disconnected. If the HOI bit (U77, bit 11) is set, “LINE IN USE” is reported
upon intrusion.
%V2 Automatic Line Status Detection—Adaptive Method.
Description: Before going off-hook with the ATD, ATO, or ATA commands, the Si2457/34/15 com-
pares 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 Si2457/34/15 to eliminate errors due to 50/60 Hz interference and also adapt
to relatively 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 "Off-Hook Intrusion Detection" on page 18) operates normally. In addition, the Si2457/34/15 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 11. Extended AT% Command Set (Command Defaults in Bold) (Continued)
Command Action