Specifications

AN93
Rev. 0.8 87
U77 (GEN2)
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 62.)
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
b
(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
b
, 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
b
(default) disables AutoOvercurrent. If
enabled and an overcurrent condition is detected, the
dc termination switches to 800 Ω, 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 62.)
U78 (GEN3)
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 63.)
Bits 15:14 (IB) controls intrusion blocking after dialing
has begun. Table 63 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
b
.
(See Table 63.)
Table 62. 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.
9AOCAutoOvercurrent.
0 = Disable.
1 = Enable.
8:0 OHT[8:0] Off-Hook Time (1 ms units) 30 ms default.
Table 63. U78 Bit Map
Bit Name Function
15:14 IB Intrusion Blocking.
00 = No intrusion blocking.
01 = Intrusion disabled from start of dial to end of dial.
10 = Intrusion disabled from start of dial to IS register time-out.
11 = Intrusion disabled from start of dial to “CONNECT XXX”, “NO DIALTONE”, or “NO CAR-
RIER”.
13:8 Reserved Read returns zero.
7:0 IS Intrusion Suspend (500 ms units) default = 0 ms.