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Passport 2®/Passport 2 LT™ Service Manual
0070-10-0441
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Theory of Operation
Passport 2 Passive Display/Keypad Interface Board
2.13
Passport 2 Passive Display/Keypad Interface Board
2.13.1
Overview
This board provides interface and support for the Passive Display, an SPI interface to a 4 x 8
matrix keypad, optical encoder and LED’s. It also provides connection for a speaker.
2.13.2
Detailed Description
CPLD Interface to the CPU Board VIA SPI
The purpose of the CPLD (U1) is to interface to, and scan for, key presses on the front panel
keypad. The method of communicating with the CPLD is the SPI port of the 68HC916X1
communications processor on the CPU control board (670-00-0674). The SPI interface is a
serial interface with separate serial data and clock. Data can flow in either direction using
the common clock. The communications processor is set as the master device and the CPLD
can only be a slave.
Video Display Connections
Connectors J12, J13 and J14 are for the passive display. J12 and Jl3 are connectors for the
display data lines and power, J14 is for the inverter. Data Lines LD0 through LD7 and UD0
through UD7 originate from the video processor and are driven by 5V logic from the
FCT162373T buffer line driver. The data lines are terminated with 61.9 ohm resistors and
filtered with 68pF capacitors to ground to prevent ringing.
Speaker Connection
The system speaker is connected to J2. The Passive Display/Keypad Interface Board
functions as a pass through for this signal.
Encoder Connection
The optical encoder for the keypad is connected to J4. Phase signals (CHA/CHB) and the
switch contact signal (SW) are passed through the Passive Display/7Keypad Interface Board
to an ADC on the CPU board.
VDD Control Circuit
The board employs a P-Channel FET together with a NPN Transistor to provide power
switching for the Passive Display’s 12V excitation. The FET is controlled by the transistor
which is switched on and off by the VIDPWR* signal from the CPU board. The circuit also
provides power filtering using an LC filter to reduce the in-rush current drawn by the display.
JTAG Connection
The board is equipped with JTAG Connector, J9 for in-circuit programming of the Keypad
Scanning CPLD.
Содержание Passport 2
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Страница 154: ...Printed in U S A 0070 10 0441 Rev AG December 1 2008...