Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 163)

AN93
Rev. 1.3 163
The ISOmodem has an internal analog-to-digital converter used to monitor the loop voltage when on-hook and
loop current when off-hook to check for parallel devices going off-hook. The host measures loop voltage or current
by reading U79 [4:0] (LVCS). To set the ISOmodem to monitor loop voltage in the on-hook state, the host issues
the following commands:
To set the ISOmodem to monitor loop current, the host issues the following commands:
Table 102. Intrusion Detection
Register Bit(s) Name Function
U70 10 PPDM Parallel Phone Detect
Mask
U70 2 PPD Parallel Phone Detect
U76 15:9 OHSR Off-Hook Sample Rate
U76 8 FACL Force ACL
U76 7:5 DCL Differential Current
Level
U76 4:0 ACL Absolute Current Level
U77 15:12 IST Intrusion Settling Time
U77 11 HOI Hang-Up On Intrusion
U78 15:14 IB Intrusion Blocking
U78 7:0 IS Intrusion Suspend
U79 4:0 LVCS Line Voltage/Current
Sense
U83 15:0 NOLN No Line Threshold %V1
U84 15:0 LIUS Line-in-use Threshold
%V1
U85 15:0 NLIU Line-in-use/No Line
Threshold %V2
Command Function
AT:R79 Host reads the loop voltage
from the LVCS Register U79
bits 4:0 while the modem is
on-hook.
Command Function
ATH1 To go off-hook
AT:R79 Host reads loop current from
the LVCS Register U79 bits
4:0 while the modem is off-
hook.