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Software Safety Features
Hardware-related Software Safety Features
Program Memory Check
At power up and at regular intervals thereafter,
the program memory is tested by calculating
a Cyclic Redundancy Code (CRC) on the
program and then comparing it with the CRC
stored with the program. If the stored and
calculated CRCs do not match, the software
will turn on a continuous two-tone audible
alarm and stop all drug delivery.
RAM Memory Check
At power up, the random access memory is
checked. A particular bit pattern is written to
and read from each address in the RAM. If the
read data is different from the written data, the
software will turn on a continuous two-tone
audible alarm and stop all drug delivery.
Motor Circuit Check
At power up and at regular intervals thereafter,
the motor circuit is checked to ensure that no
power is being applied to the motor unless the
motor is actually on. If the software detects
power being applied to the motor at any other
time, it will sound a continuous two-tone
audible alarm and will no longer attempt to
deliver medication. During every pump
activation, the software checks to see whether
the motor completes one activation. If the
motor fails to turn, or fails to complete a cycle,
the software will turn on a continuous two-
tone audible alarm and stop all drug delivery.
Keyboard Encoder Check
Every time the software receives data from the
keyboard encoder, it is checked. If the data is
not of the proper form, the software will turn
on a continuous two-tone audible alarm and
stop all drug delivery. The DOSE key has two
independent signal lines to prevent single fault
failures.
Data Handling Software Safety Features
Data Stored in RAM
Before use, data associated with delivery and
stored in RAM is tested by calculating a CRC
on the data and then comparing it with the
CRC stored with the data. If the stored and
calculated CRCs do not match, the software
will turn on a continuous two-tone audible
alarm and stop all drug delivery.
Data Stored in EEPROM
Before use, data associated with delivery and
stored in EEPROM is tested by calculating a
CRC on the data and then comparing it with
the CRC stored with the data. If the stored and
calculated CRCs do not match, the software
will turn on a continuous two-tone audible
alarm and stop all drug delivery.
Data Stored in NOVRAM
Before use, data associated with delivery and
stored in NOVRAM is tested by calculating a
CRC on the data and then comparing it with
the CRC stored with the data. If the stored and
calculated CRCs do not match, the software
will turn on a continuous two-tone audible
alarm and stop all drug delivery.
Data Used in Calculations
Calculations on data used in some way to
control the delivery of drug are performed
redundantly. The two calculated values are
then compared. If the two values do not match,
the software will turn on a continuous two-
tone audible alarm and stop all drug delivery.
Timer Data Registers
The data stored in the timer control register is
checked at regular intervals. If the data is not
correct, the software will turn on a continuous
two-tone audible alarm and stop all drug
delivery.