Motorola SSETM 5000 - Manual (Page 54)

November 11, 2004 6881094C12-A
2-32 Theory of Operation: VOCON Board
Programmable side buttons SB1, SB2, and SB3 are active-low (activated when side button voltage
is 0V). When the side buttons are not pressed there are 2 V on the respective lines. S1 is a binary-
coded switch. The output pins from U1, which are connected to GPIO pins on the dual-core
processor, provide a four-bit binary word (signals RTA0, RTA1, RTA2, and RTA3) to the MCU,
indicating to which of the 16 positions the rotary is set.
2.5.5 VOCON Audio Paths
This section describes the VOCON transmit and receive audio paths.
2.5.5.1 Transmit Audio Path
Refer to Figure 2-11 . The internal microphone audio enters the VOCON board through pin 8 of the
M102 contact, and the internal microphone bias is set by circuitry that includes R531, R533, C519
and C521. The internal microphone signal is connected to the MICIN_NEG pin, which is the input
terminal on the GCAP II IC internal op-amp A3. The gain of the A3 op-amp is set by the values of
R540, R555, and the resistance of EEPOT U509 (digital potentiometer), which is programmed by
dual-core processor GPIO lines.
The external microphone audio enters the VOCON board through the remote connector J102, pin
10, and the external microphone bias is set by circuitry that includes R563, R565, C547, and C548.
The external microphone signal is connected to the AUX_MIC_NEG pin, which is an input terminal
on the GCAP II IC internal op-amp A5. The gain of the A5 op-amp is set by the values of R566,
R561, and the resistance of the EEPOT U509.
The dual-core processor, through the SPI bus, programs a multiplexer to select one of the
microphone signals. Then, the selected amplified microphone signal goes through a programmable
gain amplifier before it goes to the CODEC for A/D conversion. The resulting digital data is filtered
and sent to the DSP on the SAP CODEC_TX line from the GCAP II IC TX pin. After additional
filtering and processing, the DSP sends the data-out from the STDB pin to the RF interface
connector P201 pin 4 (TX_DATA), which is connected to the DAC U203 on the transceiver board.