
TB9100 Reciter Service Manual
Network Circuitry
71
© Tait Electronics Limited January 2006
5.4.3
Serial Interfaces
Two separate Multi-channel Buffered Serial Ports (McBSP) are used to
communicate with the ASIF CODEC chip (McBSP0) and the reciter DSP
(McBSP1). A third McBSP channel (McBSP2) is available, but is not used
in the ASIF design. These ports implement a high-speed synchronous serial
interface with bi-directional data transfer. The transmit and receive
operations on these ports may operate independently, but, in most
applications, they are operated at the same data and sample rates. Reference
14 should be consulted for details of the operation of these McBSP ports.
McBSP0 connects to the CODEC (see
“CODEC Digital Interfaces” on
page 79
) and is used for transferring audio data to and from that chip at the
audio sample rate, ie. 8.0kHz. The CODEC data is formatted as 15-bit
linear PCM code, but is transmitted, msb first, on port DX0 using a 16-bit
frame for ease of handling within the DSP. Data is simultaneously received
on port DR0, enabling full-duplex operation. The bit rate is 2.048 MHz and
the frame sync rate is 8.0KHz, ie. the sample rate.
As the CODEC chip is a client device, McBSP0 is configured as a server
device, ie. it generates the clocks and sync signals for the CODEC.
The CODEC does not require separate transmit and receive clocks, so a
clock output is generated on the transmit clock output, CLKX0, and fed
back to McMSP receive clock input, CLKR0, as well as the CODEC clock
input, PCMCLK. To synchronize the data frames within the bit stream, the
DSP outputs a transmit frame sync signal, FSX0, which is fed back to the
McBSP receive sync input, FSR0, as well as the CODEC sync input,
PCMSYNC.
McBSP1 is used to transfer data to and from the reciter DSP.
The interconnections are detailed in
Table 5.8
. The receive port lines
(DR1, FSR1, CLKR1) are configured as inputs, as the reciter DSP
generates all the relevant clock and sync signals. On the transmit side, the
McBSP outputs all the signals (CLKX1, FSX1, DX1) for reception by the
reciter DSP. The bit rate is 12.8 Mbps. The frame sync line is active high for
one bit following a 16-bit data transfer.
5.5
I/O Buffers
5.5.1
RS-232 Interface
A basic RS-232 interface, supporting only the RxD and TxD lines, is
provided on the ASIF for connection to external serial devices such as
dispatchers, terminals and PCs. The interface is configured as DCE mode
and connection is made through a rear panel DB9 socket, which is pin-out
compatible with IBM PC serial cables.
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