Datascope Passport 2, Руководство по обслуживанию

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Passport 2®/Passport 2 LT™ Service Manual 0070-10-0441 2 - 21
Theory of Operation TFT Display / Monochrome Interface Board and Keypad Board (P/N 0670-00-0686 or 0670-00-0726)
2.3 TFT Display / Monochrome Interface Board and
Keypad Board (P/N 0670-00-0686 or 0670-00-0726)
Overview
This board provides interface and support for four different displays, an SPI interface to 4 X
8 matrix keypad, optical encoder and LED’s. It provides connections for an external speaker
and inverter for the display.
2.3.1 The EPLD 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, 0670-00-0674. 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.
The method used to scan the keypad, which is a 4 row (J11) with up to 8 columns (J10), is a
“walking zero” pattern. This means that 3 of the 4 row/lines will always be a logic “1” with
one line driven low. In a complete cycle, each line will sequentially be driven low, driving a
different row on the keypad.
2.3.2 Video display connections
The J5 connector is the decoded video for the TFT color LCD / monochrome display based on
the board’s configuration. The 3.3 VDC input power requires additional filtering.
2.3.3 TFT Inverter Connection
The inverter for the monochrome or TFT display is connected to J3. This inverter uses the
fi12V2 voltage and is controlled via a 5V CMOS compatible signal.
2.3.4 Speaker connection
The system speaker is connected to J2. The Interconnect Board functions as a pass through
for this signal.
2.3.5 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 interconnect board to ADC on the CPU
board.