Bose 3-2-1 Handbuch zur Fehlersuche - Seite 9

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3.2 Interface Blocks

3.2.1 Vacuum Fluorescent Display (VFD)

This vacuum fluorescent display is a custom, stand-alone VFD module manufactured by

Futaba. It includes the VFD glass assembly, as well as all power supply and control/refresh

electronics, and a ribbon cable interconnect to the console main board.

The console VFD module interface with the Main board is by a flexible cable via connector

J6500 [sheet 13, B8] which has 5-pin as listed in following table:

J6500

Signal

+12V

Strobe/

Ground

Clock

Data

Note: (1) There is a buffer, U6802 with open collector between VFD and the CS98200. The

buffer is required to level-shift the 3.3V logic levels associated with the SPI interface to the 5V

logic levels required by the VFD module.

(2) The VFD module has built-in 1.5K Ohm pull-up resistors on the Clock, Data and Strobe

signals. There are no such pull-ups on the console Main Board; therefore, these signals will not

be measurable at connector J6500 unless the VFD is attached.

3.2.2 Button Board

The console has 6 buttons on the top leading edge. The buttons are physically located on a

small assembly which connects to the Main Board via ribbon cable into J6700 [sheet 8, D8].

Software continually monitors these buttons to detect and de-bounce a key press. Pull-down

resistors are provided to hold KEY inputs to logical 0 (ground) when no buttons are pressed.

Interconnections to the buttons are in the form of a 2x3 row/column matrix of key closures.

Each button is therefore identified by its unique row/column position.

The arrangement of buttons on the front of the console is as follows. Each circular button

represents a key closure which shorts a given KEYOUT row signal to a given KEYIN column

signal when a button is pressed. For example, ON/OFF shorts the KEYOUT0 signal to KEYIN0

when pressed:

KEYOUT0

ON/OFF

KEYIN0

THEORY OF OPERATION

+12V supply for the module.

Strobe for serial protocol (low when sending VFD data).

Power supply/signal ground.

Clock for serial protocol. Normally high here at the connector.

Data for serial protocol. Normally high here at the connector.

KEYOUT1

SOUR

Function

VOLUME

KEYOUT2

EJECT

ENTER

KEYIN1