Fluke Biomedical 945A - Manual (Page 61)

Table 4-22. Sensitivity Select Read Functions
Data Bit Function
D0 Serial data from E2 PROM
D1 Anti-Jam
D2 (not used)
D3 JP3-5 (IN) Inhibit alarms during check source operation
(OUT) Alarms active during check source operation
D4 JP3-4 (IN) Fails in five minutes with a 0.00 mR/h value displayed
(OUT) Does not fail
D5 JP3-3 (OUT) Auto alarm acknowledge, after counts return to normal
(IN) Manual Reset
JP3 jumper IN MPU reads a low (0)
JP3 jumper OUT MPU reads a high (1)
Switch Inputs
Octal inverting buffer U62 functions as an interface to provide the status of the front panel control
switches to the internal data bus and MPU. U62 responds to address 4000. The switch input bit
assignments are listed in table 4-23.
Table 4-23. Switch Input Bit Assignments (U62)
Data Bit Function
D0 Alarm Acknowledge (Latched)
D1 Check Source (Latched)
D2 (Spare)
D3 (Spare)
D4 Rate-of Rise (when applicable)
D5 Warn Alarm
D6 High Alarm
When a switch is pressed, the appropriate input to U62 is pulled low. When U62 is read by the MPU, a
high (1) is available on the data bus. When no switches have been pressed, all outputs (U62) will be low
when read. U63 is a latch which latches switch data from the check source and alarm acknowledge
switches. The MPU controls the clear switch latch signal to reset U63. The circuit comprised by S1, D1,
and R11 is a remote alarm acknowledge. R11 is selected to allow a 20 mA signal to flow through the S1
infrared diode when a given voltage is present on the J9 remote acknowledge input. When this voltage is
present, the S1 infrared diode is forward biased, causing the S1 phototransistor to conduct. This
effectively forces a low (0) to U63-10, setting the alarm acknowledge bit.
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