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DS3171/DS3172/DS3173/DS3174
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lists the PAIS decodes for various payload AIS enable modes.
Table 10-19. Payload (Downstream) AIS Enable Modes
PAIS[2:0]
When AIS is sent
AIS Code
000 Always
UA1
001
When LLB (no DLB) active
UA1
010
When PLB active
UA1
011
When LLB(no DLB) or PLB active
UA1
100
When LOS (no DLB) active
UA1
101
When OOF active
UA1
110
When OOF, LOS. LLB (no DLB), or
PLB active
UA1
111 Never
none
10.5.4 Loop Timing Mode
Loop timing mode is enabled by setting the
PORT.CR3
.LOOPT bit. This mode replaces the clock from the TCLKIn
pin with the internal receive clock from either the RLCLKn pin if the RX LIU is disabled, or the recovered clock from
the RX LIU if it is enabled. The loop-timing mode can be activated in any framing or line interface mode.
10.5.5 HDLC Overhead Controller
The data signal to the receive HDLC controller will be forced to a one while still being clocked when the framer
(DS3, E3), to which the HDLC is connected, detects LOF or AIS. Forcing the data signal to all ones will cause an
HDLC packet abort if the data started to look like a packet instead of allowing a bad, and possibly very long, HDLC
packet.
10.5.6 Trail Trace
There is a single Trail Trace controller for use in line maintenance protocols. The E3-G.832 framer has access to
the trail trace controller.
10.5.7 BERT
There is a Bit Error Rate Test (BERT) circuit for each port for use in generating and detecting test signals in the
payload bits. The BERT can generate and detect PRBS patterns up to 2^32-1 bits as well as repeating patterns up
to 32 bits long. The generated BERT signal replaces the data on the TSERn pin in SCT modes when the BERT is
enabled by setting the PORT.CR1.BENA.
When the BERT is enabled The TDENn and RDENn pins will still be active but the data on the TSERn pin will be
discarded.
10.5.8 SCT port pins
The SCT port pins have multiple functions based on the framing mode the device is in as well as other pin mode
select bits.
10.5.8.1 Transmit SCT port pins
The transmit SCT pins are TSOFIn, TSERn, TSOFOn / TDENn, and TCLKOn / TGCLKn. They have different
functions based on the framing mode and other pin mode bits. Unused input pin functions should drive a logic zero
into the device circuits expecting a signal from that pin. The control bits that configure the pins’ modes are
FM[2:0],
TPFPE,
TSOFOS and
TCLKS.