MTR3000 Wireline: Functional Theory Of Operation 8-5
8.3.1.6 Backplane SPI Bus
The backplane SPI interface is used as the primary communication link between the Station Control
Board and the Wireline board. This interface is used for configuring and upgrading the Wireline
board.
8.3.1.7 GPIO Signals
The GPIO signals comprise both input and output signals that the Wireline FPGA uses to
communicate control information with the Station Control Module. Inputs to the Wireline board inform
the Wireline FPGA when an RF carrier has been detected or a PL tone has been decoded. Output
signals from the Wireline board are used to select the base station/repeater transmit frequency and
activate the alternate CPS defined GPIO functions. These signals are generally activated in
response to decoded DC currents or tone sequences. The PTT GPIO signal functions as both an
input and an output. When used as an output, the signal will key up the base station/repeater’s
transmitter. When a backplane PTT condition is present, but not driven by the Wireline board, the
signal may function as an input. This allows the Wireline to switch the direction of audio when
configured for 2-wire half-duplex with no remote control.
900 Ω For Brazil
320 Ω + (230 nF || 1050 Ω) For United Kingdom
200 Ω + (100 nF || 680 Ω) For China
900 Ω || 30 nF For legacy MTR2000
Table 8-2 Impedance supported by Wireline board (Continued)
Option Functionality
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