Service Manual

MM-E 2072-09333-00
2-22
the DSP host port interface, and by a few discrete control lines. The RAM U6038 connected to
the DSP, address and data buses, is used by the DSP to store temporary variables and data.
The DSP has two ESSIs: ESSI 1 is used to connect to the codec U6040, and ESSI 0 is used to
connect to the DSM, U6000.
The operations performed by the DSP are determined by the program data loaded from the
microcontroller through the HPI. After processing the data stream received from the codec, the
DSP sends the resulting data stream, through ESSI 0, to the DSM, U6000.
c. DSM Functions. The DSM is a special-purpose digital processing component that converts the
incoming serial data stream to an analog signal, DSM_OUT. U6000 uses the same clock
frequency as U6042, 16.8 MHz.
The DSM_OUT signal is generated by an A/D converter, comprising a weighted network of
resistors connected to DSM FIR outputs.
The resulting signal is the transmit IF, an SSB (or AME) signal (in accordance with the
modulation mode selected by the user), on a 1.05 MHz virtual carrier.
2-4.2.2 Receive Path
a. The receive path of the DSP subsystem receives the digital stream representing the third IF
signal, generated by the serial output A/D converter, U1115. This stream, A_D_DATA, is
connected to the receive input, SRD0, of ESSI 0. U1115 conversion rate and timing are
synchronized by the clock and strobe signals, SR_CLK and CONVST, provided by the DSP.
The DSP can also control the operation mode of U1115, via the serial data stream SR_DATA.
b. The DSP processes the received data streams, and converts it to a data stream that represents the
demodulated IF signal. This stream is sent via ESSI 1 to the input, DIN, of the digital/analog
conversion section of the codec U6040.
The resulting analog signal is provided as a balanced signal at the OUTP and OUTM outputs.
These outputs are connected via the RX_AUDIO line to the audio receive path (para. 2-4.1.2).
2-4.3 ISB Option
Refer to Figure A-1.E.
The ISB option includes a codec, U6088, similar to U6040.
a. The A/D conversion path of U6088 processes the slave sideband signal, received from the
ACCESSORY connector via EXT_TX_AUDIO_ISB line. This signal is amplified and filtered
by U6089. The resulting data stream is sent to the DSP via the HYB_ESSI_STD line.
b. The D/A conversion path of U6088 receives the serial HYB_ESSI_SRD data stream from the
DSP, and converts it to a balanced audio signal. This signal is amplified by U6089, and sent to
the ACCESSORY connector via the EXT_RX_AUDIO_ISB line.
2-4.4 IF and RF Transmit Path
Refer to Figure A-1.M, Figure A-1.N, Figure A-1.P.
a. The 1.05 MHz signal generated by the DSM passes through a bandpass filter to the IF RX/TX
switch. In the transmit mode, CR1905 is forward biased and connects the signal to the second
mixer, U1108.
b. U1108 mixes the signal with the local oscillator signal, TX_SEC_INJ, provided by
synthesizer 2 (para. 2-4.7.3). The resulting signal, TRANS_IF, at 45.1 MHz, is applied to the
transmit section of the bidirectional IF amplifier, Q1006.
c. The amplified signal passes through the crystal filters FL2, FL1. The filtered signal bypasses the
first IF amplifier, Q1001, via the PIN diode switch CR1011, CR1012, and reaches the first
mixer, U1000.