MT9079
8) When CRC-4 multiframing has been achieved,
the primary basic frame alignment and resulting
multiframe alignment will be adjusted to the basic
b) Remote loopback (RxA and RxB to TxA and TxB
respectively at the PCM 30 side). Bit RLBK = 0
normal; RLBK = 1 activate.
frame alignment
determined during CRC-4
synchronization. Therefore, the primary basic frame
alignment will not be updated during the CRC-4
multiframing search, but will be updated when the
CRC-4 multiframing search is complete.
MT9079
Tx
System
PCM30
DSTo
Rx
Channel Signalling
c) ST-BUS loopback (DSTi to DSTo at the system
side). Bit SLBK = 0 normal; SLBK = 1 activate.
When control bit TxCAS is low the MT9079 is in
Channel Associated Signalling mode (CAS); when
TxCAS is high it is in Common Channel Signalling
(CCS) mode. The CAS mode ABCD signalling
nibbles can be passed either via the micro-ports
(RPSIG = 1) or through related channels of the
CSTo1 and CSTi2 serial links (RPSIG = 0), see
Figure 4. Memory page five contains the receive
ABCD nibbles and page six the transmit ABCD
nibbles for micro-port CAS access.
MT9079
Tx
DSTi
System
PCM30
DSTo
d) Payload loopback (RxA and RxB to TxA and TxB
respectively at the system side with FAS and NFAS
operating normally). Bit PLBK = 0 normal; PLBK = 1
activate. The payload loopback is effectively a
physical connection of DSTo to DSTi within the
MT9079. Channel zero and the DL originate at the
point of loopback.
In CAS operation an ABCD signalling bit debounce
of 14 msec. can be selected (DBNCE = 1). This is
consistent with the signalling recognition time of
CCITT Q.422. It should be noted that there may be
as much as 2 msec. added to this duration because
signalling equipment state changes are not
synchronous with the PCM 30 multiframe.
MT9079
DSTi
Tx
If basic frame synchronization is lost (page 3,
address 10H, SYNC = 1) all receive CAS signalling
nibbles are frozen. Receive CAS nibbles will become
unfrozen when basic frame synchronization is
acquired.
System
Rx PCM30
DSTo
e) Local and remote time slot loopback. Remote
time slot loopback control bit RTSL = 0 normal; RTSL
= 1 activate, will loop around transmit ST-BUS time
slots to the DSTo stream. Local time slot loopback
bits LTSL = 0 normal; LTSL = 1 activate, will loop
around receive PCM 30 time slots towards the
remote PCM 30 end.
When the SIGI interrupt is unmasked, IRQ will
become active when a signalling nibble state change
is detected in any of the 30 receive channels. The
SIGI interrupt mask is located on page 1, address
1CH, bit 0; and the SIGI interrupt vector (page 4,
address 12H) is 01H.
MT9079
Loopbacks
Tx
DSTi
System
PCM30
In order to meet PRI Layer 1 requirements and to
assist in circuit fault sectionalization the MT9079 has
six loopback functions. These are as follows:
DSTo
Rx
The digital, remote, ST-BUS and payload loopbacks
are located on page 1, address 15H, control bits 3 to
0. The remote and local time slot loopbacks are
controlled through control bits 4 and 5 of the per time
slot control words, pages 7 and 8.
a) Digital loopback (DSTi to DSTo at the PCM 30
side). Bit DLBK = 0 normal; DLBK = 1 activate.
MT9079
DSTi
Tx
System
PCM30
DSTo
4-251
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