
TB9100 Reciter Service Manual
Network Circuitry
57
© Tait Electronics Limited January 2006
Time-Division
Multiplexed (TDM)
Port and Time Slot
Assigner (TSA)
Communication between the DSPs in the ASIF and reciter takes place over
a PCM highway. This is a TDM bus supporting bi-directional full-duplex
synchronous data transfers. The PCM highway contains six signals: transmit
data, transmit frame sync., transmit clock, receive data, receive frame sync.
and receive clock. These are also connected to the MPC’s time slot assigner’s
(TSA) pins and DSP pins as shown in
Table 5.8
. The MPC has two TSA
ports but only one is used in the ASIF.
Data transfers take place in periodic “frames”, which are typically a multiple
of the DSP software’s sample rate. Within each frame, a number of “time
slots” exist, each usually 8 or 16 clocks wide. The position of a time slot is
determined relative to the frame sync signal, which signifies the start of a
frame.
The serial data stream and synchronization signals for SMC2 are routed
through the MPC’s TSA. The TSA logic selects the data stream from a
particular time slot, or combination of time slots, and routes it to the receiver
data input of the SMC. Conversely, the TSA routes the transmit data output
from the SMC and inserts the data stream into the selected time slot(s) in the
frame. The transmit data outputs of the TSA and the DSPs are tri-stated
when they are not active so that they can share the PCM highway.
Along with the data streams, the TSA routes the transmit and receive clocks
to the SMC along with the transmit and receive sync signals. Transmitted
bits are shifted out on the positive edge of the transmit clock and received
bits sampled on the negative edge of the receive clock
Serial Peripheral
Interface (SPI)
The SPI port is a simple full-duplex synchronous serial interface that
connects to the SIO port on the reciter RISC. A data transfer between
devices using SPI requires that one device be defined as the server and the
other as a client device. The reciter RISC is the server device, so the MPC’s
SPI is configured as a client device. The MPC’s SPI effectively emulates the
SIO I/O expansion circuitry present on the analog SIF.
Table 5.8
PCM Highway Connections
PCM Highway Signal
ASIF DSP Pins
(I/O direction)
Reciter DSP Pins
(I/O direction)
MPC Time Slot
Assigner Pins
Transmit data
(O/P)
(O/P)
L1TxDA (O/P)
Transmit frame sync
(I/P)
(O/P)
L1TsyncA (I/P)
Transmit clock
(I/P)
(O/P)
L1TclkA (I/P)
Receive data
(I/P)
(I/P)
L1RxDA (I/P)
Receive frame sync
(I/P)
(O/P)
L1RsyncA (I/P)
Receive clock
(I/P)
(I/P)
L1ClkA (I/P)
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