Chapter 2 THEORY OF OPERATION
2 - 14
The keyboard is scanned under software control via U11-PB0 to U11-PB5 for the row
scanning. The columns are scanned via U12-P1.0 to U12-P1.3. No switches are present
at the shaded sections of the table.
2.2.12.2 LED Status Indicators
The LED status indicators are located above the keypad. They provide an alternate
method of communication between the user and the pump.
• “RUN”, “STANDBY”, “LOCK”, “ALERT”, “BATTERY”
There are three “RUN” LEDs as well as the “STANDBY”, “LOCK”, “ALERT” and
“BATTERY” LEDs. They have different behavior modes depending on the mode of
operation of the pump. They are controlled by the master CPU through the “I2C_2” serial
interface bus and U10.
• “SYSTEM”
The “SYSTEM” LED is controlled in a manner similar to the other LEDs except that it is
also controlled by the line “SYS_FS*” from the fail-safe latch logic. It is lit whenever the
fail-safe latch is in the set state.
• “ON CHARGE”
The “ON CHARGE” LED is controlled under master CPU control through U11-PC2
“CHRG_LED” for the purposes of lamp test. It is also powered by the presence of charging
voltages from the battery charge regulator via “CHARGER+”. It gives an indication of the
charger being active.
2.2.12.3 Syringe Drive Potentiometer Position and Capture Detector
J7 connects the digital board to the Drive Potentiometer Position Sensor. The signal
“LINEAR_POS” is used by the master CPU to determine proper drive movement, end of
syringe and near end of syringe alerts and syringe plunger capture. This signal is
calibrated by using a series of gages in the syringe drive mechanism with the pump in
calibration mode.
Plunger capture is performed by mechanically lifting the potentiometer wiper when the
syringe plunger is not captured in the plunger driver. R59 will then pull the “LINEAR_POS”
signal immediately to zero volts indicating a loss of plunger capture.
Proper drive movement is accomplished by an algorithm that assures that the
LINEAR_POS signal does progress according to the movement that is expected from the
primary and secondary lead screw encoders. This is a tertiary check on the movement of
the syringe plunger and also assures that the plunger drive mechanism has properly
captured the lead screw with the half nuts.
2.2.12.4 Sensor Power
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