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3-20 Theory of Operation: Transceiver Board

3.1.4.8 Port Expander

U703 is a port expander that is controlled by the auxiliary SPI of the Trident IC; pins A7

(ASPI_DATA), B7 (ASPI_CLK) and C6 (ACE1_GPO7). Data sent on the main SPI bus with a specific

header, tells the Trident IC to pass the data (via the auxiliary SPI lines) onto the port expander SPI

lines, pins 32 (SCLK), 33 (DIN) and 34 (CS). The port expander then translates this auxiliary SPI

data and turns on and off the select lines for the various VCOs, switches (that select the correct RF

path for either VHF, UHF Range 1 or 7/800) and other logic external to the FGU. Table 3-3 below

shows the logic settings for the port expander for the various bands.

Table 3-3. Port Expander Pin Settings

VHF TX

PIN NO.1234567 8 9 10 12 13 14 15

LOGIC 000000H H000000

PIN NO. 16 17 18 19 21 22 23 24 25 26 27 28 29 30

LOGIC 0 H000H H H0H0000

VHF RX

PIN NO.

1 2 3 4 5 6 7 8 9 1012131415

LOGIC H H H H0000000000