THEORY OF OPERATION Model 360E Instruction Manual
10.4.1.4. Keyboard/Display Interface Electronics
FRONT PANEL

Keypad

Decoder

Key Press
Detect
KEYBOARD
Beeper
Sample LED
(Green)
Cal LED
(Yellow)
Fault LED
(Red)
Display Data
Decoder
Display Power
Watchdog
From 5 VDC
Power Supply
I
2
C to Relay Board
Parallel Data

2 x 40 CHAR. VACUUM

FLUORESCENT DISPLAY

Display
Controller
Display Write
Clock
Serial
Data
I2C to/from CPU
Keyboard Interrupt Status Bit

I2C Interface

2n
d
Lang.
Switch
Maint.
Switch
Optional
Maintenance
LED
Figure 10-18: Keyboard and Display Interface Block Diagram
The keyboard/display interface electronics of the M360E Analyzer watches the status of the eight front panel
keys, alerts the CPU when keys are depressed, translates data from parallel to serial and back and manages
communications between the keyboard, the CPU and the front panel display. Except for the Keyboard interrupt
status bit, all communication between the CPU and the keyboard/display is handled by way of the instrument’s
I2C buss. The CPU controls the clock signal and determines when the various devices on the bus are allowed to
talk or required to listen. Data packets are labeled with addresses that identify for which device the information
is intended.
KEYPAD DECODER
Each key on the front panel communicates with a decoder IC via a separate analog line. When a key is
depressed the decoder chip notices the change of state of the associated signal; latches and holds the state of
all eight lines (in effect creating an 8-bit data word); alerts the key-depress-detect circuit (a flip-flop IC);
translates the 8-bit word into serial data and; sends this to the I2C interface chip.
KEY-DEPRESS-DETECT CIRCUIT
This circuit flips the state of one of the inputs to the I2C interface chip causing it to send an interrupt signal to the
CPU
186 05232 Rev B3