MT89L86 Data Sheet
13
Zarlink Semiconductor Inc.
The Control register is dynamically used by the CPU to control switching operations in the MT89L86. The Control
register selects the device's internal memories and its subsections to specify the input and output channels
selected for switching procedures.
The data in the Control register consists of Split memory and Message mode bits, Memory select and Stream
Address bits. The memory select bits allow the Connect Memory HIGH or LOW or the Data Memory to be chosen,
and the Stream Address bits define an internal memory subsections corresponding to input or output ST-BUS
streams.
Bit 7 (Slip Memory) of the Control register allows split memory operation whereby reads are from the Data memory
and writes are to the Connect Memory LOW.
The Message Enable bit (bit 6) places every output channel on every output stream in message mode; i.e., the
contents of the Connect Memory LOW (CML) are output on the ST-BUS output streams once every frame unless
the ODE input pin is LOW. If ME bit is HIGH, then the MT89L86 behaves as if bits 2 (Message Channel) and 0
(Output Enable) of every Connect Memory HIGH (CMH) locations were set to HIGH, regardless of the actual value.
If ME bit is LOW, then bit 2 and 0 of each Connect Memory HIGH location function normally. For example, if bit 2 of
the CMH is HIGH, the associated ST-BUS output channel is in Message mode. If bit 2 of the CMH is LOW, then the
contents of the SAB and CAB bits of the CMH and CML define the source information (stream and channel) of the
time-slot that is to be switched to an output.
If the ODE input pin is LOW, then all serial outputs are set to high impedance. If ODE is HIGH, then bit 0 (Output
Enable) of the CMH location enables (if HIGH) or disables (if LOW) the output drivers for the corresponding
individual ST-BUS output stream and channel.
The contents of bit 1 (CSTo bit) of each Connection Memory High location is output to the CSTo pin once every
frame. The CSTo pin is a 2048 Mbit/s output which carries 256 bits. If CSTo bit is set HIGH, the corresponding bit on
CSTo output is transmitted HIGH. If CSTo bit is LOW, the corresponding bit on the CSTo output is transmitted LOW.
The contents of the 256 CSTo bits of the CMH are transmitted sequentially to the CSTo output pin and are
synchronous to the 2.048 Mb/s ST-BUS streams. To allow for delay in any external control circuitry the contents of
the CSTo bit is output one channel before the corresponding channel on the ST-BUS streams. For example, the
contents of CSTo bit in position 0 (ST0, CH0) of the CMH, is transmitted synchronously with ST-BUS channel 31, bit
7. The contents of CSTo bit in position 32 (ST1, CH0) of the CMH is transmitted during ST-BUS channel 31 bit 6.
For more detailed description of the CSTo operation, see section 6 of Application Note MSAN-123.
The V
/C bit (Variable/Constant Delay) of each Connect Memory High location allows the per-channel selection
between Variable and Constant throughput delay modes.
Initialization of the MT89L86
On initialization or power up, the contents of the Connection Memory High can be in any state. This is a potentially
hazardous condition when multiple MT89L86 ST-BUS outputs are tied together to form matrices, as these outputs
may conflict. The ODE pin should be held low on power up to keep all outputs in the high impedance condition.
During the microprocessor initialization routine, the microprocessor should program the desired active paths
through the matrices, and put all other channels into the high impedance state. Care should be taken that no two
ST-BUS outputs drive the bus simultaneously. When this process is complete, the microprocessor controlling the
matrices can bring the ODE signal high to relinquish the high impedance state control to the OE bit of the CMH
(CMH
b
0s).
A RESET pin is available for the 48-pin SSOP package. When this pin is set low for a minimum of 100 n sec, the
ST-BUS outputs are put to the high impedance state and all register contents are set to zero.
