Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 115)

AN93
Rev. 1.3 115
U77 is a bit-mapped register that controls parameters relating to intrusion detection and overcurrent detection. U77
resets to 0x401E with a power-on or manual reset (see Table 75).
Bits 15:12 (IST) set the delay between the time the modem goes off-hook and the intrusion detection algorithm
begins. This register has 250 ms increments, and the default value is 4 (1 sec).
Bit 11 (HOI) determines whether the host or modem responds to an intrusion. HOI = 0 (default) prevents the
modem from hanging-up in response to an intrusion without host intervention. In this case, the host monitors
U70 [2] (PPD) and takes the appropriate action when PPD is asserted indicating an intrusion. If HOI = 1, the
modem hangs up immediately and will not go off-hook and dial when an intrusion is detected without host
intervention. If %V
N
commands are set, HOI also causes the LINE IN USE result code upon PPD interrupt.
Bit 9 (AOC) = 0 (default) disables AutoOvercurrent. If enabled and an overcurrent condition is detected, the dc
termination switches to 800
, thus, reducing the current. If AOC = 0, the overcurrent condition is only reported by
U70 [3] (OCD).
Bits 8:0 (OHT) set the delay between the time the modem goes off-hook and LVCS is read for an overcurrent
condition. The default value for this register is 30 ms (see Table 75).
U78 is a bit-mapped register that controls intrusion detection blocking and intrusion suspend. U78 resets to 0x0000
with a power-on or manual reset (see Table 76).
Bits 15:14 (IB) controls intrusion blocking after dialing has begun. Table 76 defines the bit values and intrusion
blocking.
Bits 7:0 (IS) set the delay between the start of dialing and the start of the intrusion algorithm when IB = 10 (see
Table 76).
Table 74. U76 Bit Map
Bit Name Function
15:9 OHSR Off-Hook Sample Rate for Intrusion Detection (40 ms units).
(1 second default)
8 FACL Force ACL.
0 = While off-hook, ACL is automatically updated with LVCS value.
1 = While off-hook, ACL saves previously written value.
7:5 DCL Differential Current Level (3 mA units, 6 mA default)
4:0 ACL Absolute Current Level (3 mA units, 0 mA default)
Table 75. U77 Bit Map
Bit Name Function
15:12 IST Intrusion Settling Time (250 ms units) 1 second default.
11 HOI Hang-Up On Intrusion.
0 = ISOmodem does not automatically hang up after an off-hook PPD interrupt.
1 = ISOmodem automatically hangs up after an off-hook PPD interrupt.
10 Reserved Read returns zero.
9 AOC AutoOvercurrent.
0 = Disable.
1 = Enable.
8:0 OHT[8:0] Off-Hook Time (1 ms units) 30 ms default.