MT9075B
Preliminary Information
Loopbacks
e) Metallic Loopback (MT Loop) - The external
signals RTIP and RRING are isolated from the
receiver and the analog outputs TTIP and TRING are
internally connected to the receiver analog input. Bit
MLBK = 0 normal; MLBK = 1 activate.
In order to meet PRI Layer 1 requirements and to
assist in circuit fault sectionalization, the MT9075B
has six loopback functions. The control bits for
digital, remote, ST-BUS, payload and metallic
loopbacks are located on page 01H, address 15H.
The remote and local time slot loopbacks are
controlled through control bits 5 and 4 of the Per
Time Slot Control Words on pages 07H and 08H.
MT9075B
DSTi
System
DSTo
Tx
Rx
PCM30
a) Digital Loopback (DG Loop) - DSTi to DSTo at the
framer LIU interface. Bit DLBK = 0 normal; DLBK = 1
activate.
f) Local and Remote Time Slot Loopback. Remote
time slot loopback control bit RTSL = 0 normal; RTSL
= 1 activate, will loop around receive PCM 30 time
slots to the transmit PCM 30 time slots. Local time
slot loopback bit LTSL = 0 normal; LTSL = 1 activate,
will loop around DSTi time slots towards the DSTo
time slots.
MT9075B
DSTi
Tx
System
PCM30
DSTo
MT9075B
Tx
DSTi
b) Remote Loopback (RM Loop) - RTIP and RRING
to TTIP and TRING respectively at the PCM 30 side.
Bit RLBK = 0 normal; RLBK = 1 activate.
System
PCM30
Rx
DSTo
Error Counters
MT9075B
Tx
PCM30
Rx
The MT9075B has nine error counters, which can be
used for maintenance testing, an ongoing measure
of the quality of a PCM 30 link and to assist the
designer in meeting specifications such as ITU-T
I.431 and G.821. All counters can be preset or
cleared by writing to the appropriate locations. A
separate status page - “1 Second Status” on page
09H - latches the states of the following counters: E-
bit Error Counter, Errored Frame Alignment Signal
Counter, Bipolar Violation Counter and CRC Error
Counter on a one second interval, coincident with
the one second status bit.
System
DSTo
c) ST-BUS Loopback (ST Loop) - DSTi to DSTo at
the system side. Bit SLBK = 0 normal; SLBK = 1
activate.
MT9075B
Tx
PCM30
DSTi
System
DSTo
Associated with each counter is a maskable event
occurrence interrupt and
a
maskable counter
d) Payload Loopback (PL Loop) - RTIP and RRING
to TTIP and TRING 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 MT9075B. Channel zero and the DL
originate at the point of loopback.
overflow interrupt. Overflow interrupts are useful
when cumulative error counts are being recorded.
For example, every time the frame error counter
overflow (FERO) interrupt occurs, 256 frame errors
have been received since the last FERO interrupt. All
counters are cleared and held low by programming
the counter clear bit (master control page 01H,
address 1AH, bit 2) high. Counter overflows set bits
in the counter overflow latch (page 04H, address
16H); this latch is cleared when read.
MT9075B
DSTi
System
DSTo
Tx
PCM30
Rx
The overflow reporting latch (page 04H, address
16H) contains a register whose bits are set when
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