Specifications
AN93
82 Rev. 0.8
U68 (ITC2)
U68 is a bit-mapped register with bits 15:3 reserved.
Reading these bits returns zero. Bits 4 and 2:0 are all
read/write. (See Table 55.)
Bit 2 (BTE) = 0
b
(default) is disabled by default. When
BTE = 1
b
, the DAA automatically responds to a collapse
of the line-derived power supply during a billing tone
event. When off-hook, if BTE = 1
b
and BTD goes high,
the dc termination is increased to 800 Ω to reduce loop
current. If BTE and U70[9] (RIM) are set to 1
b
, an
interrupt from U70[1] (RI) also occurs when BTD goes
to 1
b
(high).
Bit 1 (ROV) is normally 0
b
and is set to 1
b
to report an
excessive receive input level. ROV is cleared by writing
it to 0
b
.
Bit 0 (BTD) = 0
b
normally but is set to 1 if a billing tone
is detected. BTD is cleared by writing a 0
b
to BTD.
U68 resets to 0x0000 with a power-on or manual reset.
U6A (ITC4)
U6A is a bit-mapped register with bits 15:3 and 1:0
reserved. Reading these bits returns zero. Bit 2 is read
only. (See Table 56.)
Bit 2 (OVL) is a read-only bit that detects a receive
overload. This bit is similar to U68[1] (ROV) except OVL
clears itself after the overload condition is removed.
Table 55. U68 Bit Map
Bit Name Function
15:8 Reserved Read returns zero.
7 Reserved Do not modify.
6 Reserved Do not modify.
5 Reserved Do not modify.
4:3 Reserved Do not modify.
2BTEBilling Tone Protect Enable.
0
=
Disabled.
1
=
Enabled.
1ROVReceive Overload.
0
=
Normal receive input level.
1
=
Excessive receive input level.
0BTDBilling Tone Detected.
0
=
No billing tone.
1
=
Billing tone detected (cleared by writing 0).
Table 56. U6A Bit Map
Bit Name Function
15 Reserved Read returns zero.
14 SQ1 Spark quenching. See OHS2.
13 Reserved Read returns zero.
12 SQQ Spark quenching. See OHS2.
11:3 Reserved Read returns zero.
2 OVL Overload Detected.
This bit has the same function as ROV, but clears itself after the overload has been removed.
This bit is only masked by the off-hook counter and is not affected by the BTE bit.
1 Reserved Read only, value indeterminate.
0 Reserved Read returns zero.