Tait TB9100, Service Manual, Page: 56 / 132

56 Network Circuitry TB9100 Reciter Service Manual
© Tait Electronics Limited January 2006
The data rate over this interface is transmitted at 115.2kbaud using standard
asynchronous format with one start bit, eight data bits (transmitted lsb first),
no parity, and one stop bit. Reception is similarly at 115.2kbaud; the
receiver samples the received data at 16 times the baud rate to determine the
approximate centre of the start bit, thus achieving bit synchronization.
The 16x baud rate clock is generated internally by one of the four baud-rate
generators.
To minimize software loading, the SCC incorporates 32byte FIFOs on both
the transmit and receive paths, so that the software does not have to respond
to the transmission or reception of each character. DMA is also available for
facilitating data transfers from the SCC with minimal software overhead.
Serial Management
Controllers (SMC)
The MPC contains two SMCs; SMC1 and SMC2. These are much less
flexible than the SCC and can support only three modes of operation:
UART, transparent mode and general-circuit interface mode. Consult
chapter 29 of the MPC866 user’s manual (reference 2) for a detailed
description of these modes of operation.
SMC1 is used in UART mode and connects to the rear panel RS-232 serial
port via an RS-232 transceiver (see
“RS-232 Interface” on page 71 ). In
UART mode the SMC does not provide any data FIFOs on the transmit or
receive registers; only double buffering is provided. This requires that the
data transfers from the SMC’s registers be handled on a character by
character basis by the CPM, rather than in larger blocks of characters.
The SMC UART mode also does not provide any lines for hardware flow
control (RTS, CTS). Hence, the software must provide any flow control
through XON/OFF sequences.
The lack of FIFOs and hardware flow control require that the baud rate be
limited, so that no data overflows occur with subsequent loss of characters.
Typically, the baud rate that can be handled over an SMC UART channel is
only 1/10
th
of that possible with an SCC-implemented UART channel.
The recommended maximum baud rate for the rear panel RS-232 port is
therefore 115.2kbaud.
SMC2 is used in full-duplex, synchronous transparent mode. Whilst
receiving, it simply captures a bit stream without any protocol or bit-level
manipulation and transfers that bit stream data into memory. Transmission
in transparent mode is similar, as no additional protocol overhead is added
to the bit stream. Transparent mode requires a bit clock to sample the bit
stream and transmit and receive synchronization signals to delimit the start
of each character or word sent or received.
Compared to the SCC, transparent mode on the SMC provides less
functionality, as it requires that bit clocks and synchronization signals be
provided externally. SMC2 obtains these via the MPC’s TDM interface (see
“Time-Division Multiplexed (TDM) Port and Time Slot Assigner (TSA)”
on page 57
), which routes the bit clocks and word synchronization signals
from the serial PCM stream produced by the reciter DSP.