Preliminary Information
MT9075B
Receive data may also be read by the
microprocessor port. The Rx message mode dual
port RAMs (on page 11H and 12H) have a unique
address associated with each incoming line channel.
When the processor reads any of the 32 memory
locations, it reads the last byte received from the
corresponding channel.
7, SYNC = 1), the MT9075 will automatically transmit
the RAI alarm signal to the far end of the link. The
transmission of this alarm signal will cease when
basic frame alignment is acquired.
When AUTY = 0 and signalling multiframe alignment
is not acquired (page 03H, address 10H, bit 6,
MFSYNC = 1), the MT9075 will automatically
transmit the multiframe alarm (Y-bit) signal to the far
end of the link. This transmission will cease when
signalling multiframe alignment is acquired.
Alarms
The following alarms are detected by the receiver.
Each may generate a maskable interrupt:
Interrupts
•
Remote Alarm Indication (RAI) - bit 3 (A) of
the receive NFAS;
•
Alarm Indication Signal (AIS) - unframed all
ones signal for at least a double frame (512
bits) or two double frames (1024 bits);
Channel 16 Alarm Indication Signal - all ones
signal in channel 16;
The MT9075B has an extensive suite of maskable
interrupts, which are divided into eight categories
based on the type of event that caused the interrupt.
Each interrupt category has an associated interrupt
vector described in Table 11. When unmasked
interrupts occur, IRQ will go low and one or more bits
of the interrupt vector IV7-IV0 (page 04H, address
12H) will go high. After the interrupt vector is read it
is automatically cleared and IRQ will return to a high
impedance state. The interrupt acknowledgment
function can also be accomplished by toggling the
INTA bit (page 01H, address 1AH).
•
•
•
Auxiliary pattern - 101010... pattern for at
least 512 bits;
Loss of Signal - a loss of signal condition
occurs when the receive signal is detected
with more than 127 consecutive zeros. A
loss of signal condition will terminate when
an average ones density of at least 12.5%
has been received over a period of 127
contiguous pulse positions starting with a
pulse.
Remote Signalling Multiframe Alarm - bit 6
(Y-bit) of the multiframe alignment signal.
T1 - (T1 timer bit on page 03H address 12H)
this status bit (and maskable interrupt) shall
be high when a signal that is not normal has
been received for a minimum of 100 msec.
This bit will be low when a normal signal is
being received.
All the interrupts of the MT9075B are maskable. This
is accomplished through the corresponding interrupt
mask words on page 01H (except for the HDLC
interrupt mask registers which are located on page
0BH and 0CH).
•
•
National Use Bit Interrupt Mask Word (address 19H)
Bit 7
Bit 0
C8Sa6I
- - - PRBSO PRBS SanibI SabitI
Sa6I
Sa5I
•
T2 - (T2 timer bit on page 03H address 12H)
this status bit (and maskable interrupt) shall
be high when a normal signal has been
received for a minimum of 10 msec. This bit
will be low when an abnormal signal is being
received.
Interrupt Mask Word Zero (address 1BH)
Bit 7
Bit 0
SYNI
RAII
AISI AISI6I LOSI FERI BPVO SLPI
Interrupt Mask Word One (address 1CH)
The alarm reporting latch (address 1BH page 04H)
contains a register whose bits are set high for
selected alarms. These bits stay high until the
register is read. This allows the controller to record
intermittent or sporadic alarm occurrences.
Bit 7
Bit 0
SIGI
EBI
CRCI CEFI
BPVI RCR1 RCR0 BERI
Interrupt Mask Word Two (address 1DH)
Bit 7
Bit 0
BERO AUXPI CMFO
Automatic Alarms
EBO CRCO CALNI FERO
JAI
The transmission of RAI and signalling multiframe
alarms can be made to function automatically from
control bits ARAI and AUTY (page 01H, address
Interrupt Mask Word Three (address 1EH)
Bit 7
Bit 0
- - -
11H)
When ARAI
=
0
and basic frame
MFSYI CSYNI - - -
YI
1SEC
T1I
T2I
synchronization is lost (page 03H, address 10H, bit
27
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