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Model GFC7000E Instruction Manual THEORY OF OPERATION
04584 Rev A1 178
This IC performs several functions:
• Using a dedicated digital status bit, it sends an interrupt signal alerting the CPU that new
data from the keyboard is ready to send.
• Upon acknowledgement by the CPU that it has received the new keyboard data, the I
2
C
interface chip resets the key-depress-detect flip-flop.
• In response to commands from the CPU, it turns the front panel status LEDs on and off and
activates the beeper.
• Informs the CPU when the optional maintenance and second language switches have been
opened or closed (see Chapter 5 for information on these options).
Display Data Decoder
This decoder the serial translates the data sent by the CPU (in TTY format) into a bitmapped
image which is sent over a parallel data bus to the display.
Display Controller
This circuit manages the interactions between the display data decoder and the display itself. It
generates a clock pulse that keeps the two devices synchronized. It can also, in response to
commands from the CPU turn off and/or reset the display.
Additionally, for analyzers with the optional maintenance switch is installed (See Chapter 5), the
display controller turns on an LED located on the back of the keyboard interface PCA whenever
the instrument is placed in maintenance mode.
Display Power Watchdog
The Model GFC7000E’s display can begin to show garbled information or lock-up if the DC voltage
supplied to it falls too low, even momentarily. To alleviate this, a brown-out watchdog circuit
monitors the level of the power supply and in the event that the voltage level falls below a certain
level, turns the display off, then on resetting it
I
2
C Link To The Relay PCA
While the CPU’s I
2
C communication with the relay board is also routed through the
keyboard/display interface, information passed to and from the relay board via this channel is not
recognized by, acted upon or affected by the circuitry of the keyboard/display interface.
10.5. Software Operation
The Model GFC7000E Gas Filter Correlation Carbon Dioxide Analyzer is at its heart a high
performance, 386-based microcomputer running MS-DOS. Inside the DOS shell, special software
developed by Teledyne Instruments interprets user commands via the various interfaces,
performs procedures and tasks, stores data in the CPU’s various memory devices and calculates
the concentration of the sample gas.