Hill-Rom Advanta P1600, Service Manual

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Theory of Operation
Chapter 3: Theory of Operation
Advanta™ Bed Service Manual (man168ra) Page 3 - 23
3
The analog assembly is responsible for scale readings and memory retention.
The analog circuitry is located in the weigh frame of the bed as close to the
load beams as possible. The load beams are resistive bridge sensors excited by
a regulated DC voltage. The inputs from the load cells are through connectors
P1 through P4.
The scale display P.C. board (P/N 63344) is located in the footboard, is
connected to the PPM microprocessor (P/N63217) assembly through P1, and
uses an eleven position blue cable. The display is capable of showing weight
ranges from –450 lb to +450 lb. There are six switches available for user
inputs. These are connected in a 2-row-by-3 column matrix. They perform
typical scale functions like zero, on/off, and change items.
Air Control P.C. Board—P/N 44760
Echelon Node
The Echelon node consists of an Echelon microprocessor (U1, MC143150FU,
Neuron), 32Kbyte PROM (U2), power up reset circuit (U11), 10 MHz crystal,
and an RS485 transceiver (U3). The nodes’ I/O pins, I/O_0 through I/O_3
make up a 4 bit bi-directional data bus. I/O_4 through I/O_6 are used as
address lines for the HC138 decoder. The decoder outputs are chip select lines
for the HC244A and HC240A buffers (inputs) and for the four HC175 flip-
flops (outputs). I/O_8 through I/O_10 make up the Neurowire bus. These three
signals, along with other chip select lines, are used to transmit/receive data
from the sensor/valve module in the mattress. Resistor R111 is used as a
termination load for the RS485 bus. If the air control P.C. board is not the last
node on this bus, this resistor should be removed.
Latches and Buffers
Chip select (enable) lines of the HC244A and HC240A buffers allow their
outputs to access the data bus. The buffers are used to read most of this board’s
digital inputs. The chip select (clk) lines of the HC175 flip-flops are used to
latch data already on the data bus into the flip-flops. Most of the outputs on this
board are controlled from these flip-flops.
Valve/Sensor Module Digital Control Lines
CONN_CHK (P114-13) is an input signal that determines if the user-
accessible connector (located under the foot section) is connected or not. If the
signal is LO, the cable is either disconnected or there is no logic power
available on the sensor/valve board. Relay K1 will be opened by the