User Guide

PAMS
Technical Documentation
RAE–2
Baseband
Page 2– 37
Original 02/99
Internal audio connections
The speech coding functions are performed by the DSP in the MAD2 and
the coded speech blocks are transferred to the COBBA–GJ for digital to
analog conversion, down link direction. In the up link direction the PCM
coded speech blocks are read from the COBBA–GJ by the DSP.
There are two separate interfaces between the MAD2 and COBBA–GJ: a
parallel bus and a serial bus.
The parallel bus features 12 data bits, 4 address bits, read and write
strobes and a data available strobe. The parallel interface is used to
transfer all the COBBA–GJ control information (both the RFI part and the
audio part) and the transmit and receive samples.
The serial interface between MAD2 and COBBA–GJ includes transmit
and receive data, clock and frame synchronization signals. It is used to
transfer the PCM samples. The frame synchronization frequency is 8 kHz
which indicates the rate of the PCM samples and the clock frequency is 1
MHz. The COBBA generates both clocks.
4–wire PCM serial interface
The interface consists of the following signals:
a PCM codec master clock (PCMDClk),
a frame synchronization signal to DSP (PCMSClk),
a codec transmit data line (PCMTX) and
a codec receive data line (PCMRX).
The COBBA–GJ generates the PCMDClk clock, which is supplied to DSP
SIO. The COBBA–GJ also generates the PCMSClk signal to DSP by di-
viding the PCMDClk. The PCMDClk frequency is 1.000 MHz and is gen-
erated by dividing the RFIClk 13 MHz by 13. The COBBA–GJ further di-
vides the PCMDClk by 125 to get a PCMSClk signal, 8.0 kHz.
LSB
LSB
PCMDClk
PCMSClk
PCMTxData
PCMRxData
MSB
MSB
15 14 13 12 011 10
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