Hill-Rom Advanta P1600, Service Manual

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Theory of Operation
Chapter 3: Theory of Operation
Page 3 - 24 Advanta™ Bed Service Manual (man168ra)
microprocessor so that no significant power is available at the user-accessible
connector.
The output signals SEN_SEL_A (P114-16), SEN_SEL_B (P114-17), and
SEN_SEL_C (P114-18) are used to select one of the six air pressure sensors
for which data is to be received.
The EEPROM_CS (P114-15) output enables the EEPROM to access the
Neurowire bus.
The A/D_D/A_CS (P114-3) output enables the Analog-to-Digital (A/D) or the
Digital-to-Analog (D/A) converter to access the Neurowire bus.
The DATAOUT (P114-5), DATAIN (P114-4), and CLK (P114-14) signals
make up the Neurowire bus. The CLK signal strobes data to the valve/sensor
board on the DATAIN line, and it strobes data from the valve/sensor board on
the DATAOUT line.
Again the A/D_D/A_CS and EEPROM_CS chip select lines determine which
integrated circuit on the valve/sensor board will access the Neurowire bus.
External Watchdog
The circuitry surrounding U10 is an external watchdog timer circuit. In the
event that the microprocessor locks up or gets lost, this circuit will clear all the
flip-flop outputs, and reset the Neuron. The Neuron’s software must pulse
U10-6 at least once every 30 s to keep U10-8 from going LO. A falling edge of
I/O_7 generates a 480us positive pulse at U10-6 due to C39 and R15. If I/O_7
is stuck HI or LO, the DC blocking capacitor C39 allows R15 to pull the input
of the Schmitt-Trigger Inverter LO, which keeps U10-6 LO. U10 is a
programmable timer with a 16-stage counter and internal oscillator. Upon
power up, the Q output goes HI. If MR, master reset, is constantly LO, the Q
output will oscillate at 30 s HI, and then 30 s LO. A HI on MR resets the
counter and keeps the Q output HI.
24V AC Solenoid Drivers
The circuitry surrounding U20 - U25 and Q3 - Q8 comprises the solenoid
drivers used to open and close the air valves located in the mattress
valve/sensor module.
Power for the solenoids comes from the off board 80VA, 24V AC secondary,
transformer. Fuse F2 provides primary coil protection and is sized to pass
UL544 short and overload tests. Fuse F1 provides secondary protection and is
necessary for IEC601-1 short and overload tests. Zero ohm resistors, R80