Nokia NSE-3 SERIES, Service Manual

Page: 38 / 217

PAMS
Technical Documentation
NSE–3
System Module
Original 11/97
Page 3 – 32
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 MAD2 and COBBA–GJ: a
parallel bus and a serial bus. The parallel bus has 12 data bits, 4 address
bits, read and write strobes and a data available strobe. The parallel inter-
face 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 re-
ceive data, clock and frame synchronisation signals. It is used to transfer
the PCM samples. The frame synchronisation frequency is 8 kHz which
indicates the rate of the PCM samples and the clock frequency is 1 MHz.
COBBA is generating both clocks.
4–wire PCM Serial Interface
The interface consists of 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 dividing
the PCMDClk. The PCMDClk frequency is 1.000 MHz and is generated
by dividing the RFIClk 13 MHz by 13. The COBBA–GJ further divides the
PCMDClk by 125 to get a PCMSClk signal, 8.0 kHz.
LSB
LSB
PCMDClk
PCMSClk
PCMTxData
PCMRxData
MSB
MSB
15 14 13 12 0 11 10
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