Electrical System
Chapter 3: Theory of Operation
All of the caregiver control functions revolve around the microcontroller on
the standard caregiver control board. This is an 8051 variant with internal 32K
flash program, 256 + 1.2K EEPROM data memory, and 8 channels of A/D.
External to the microcontroller are the CAN transceiver, watch dog reset
circuit, serial I/O devices, and analog mux for interface to the microcontroller's
A/D converter.
Digital switch inputs and LED outputs are read and set serially. The serial
interface is SPI compatible and transfers data to and from the embedded
controller.
Three LEDs are provided on the standard caregiver control board to indicate
error conditions for troubleshooting.
Switch inputs that control bed motion are redundantly read with the
microcontroller's A/D converter by analog multiplexers. For these switches,
both analog and digital readings must be valid for a network message to be sent
indicating a switch press.
Intelligence for actions pertaining to the caregiver control system resides in
other bed modules. It reads the appropriate network variables for indicator
updates and sends the status of switches to the appropriate module by network
variable updates.
Patient Pendant
The patient pendant works on SPI communication. The pendant has a universal
clock connected at pin 1 of the P1 connector. The clock provides a rising logic
edge to move data into and out of the pendant.
PENDANT_CS is the pendant select line, which is connected at pin 2 of the P1
connector. The PENDANT_CS line will allow the user request to be read.
On pin 3 of the P1 connector is the Nurse Call connection, when the switch is
pressed the bed places a call to the nurse.
GND is pin 4 of the P1 connector, which is logic, ground for the pendant.
Power is supplied to the pendant by the P3200 central logic board. The logic
board provides a pre-regulated 8 VDC +/- 10% referenced to signal GND at
400mA max, 200mA typical. VCC is pin 6 of the P1 connector, which supplies
the pendant with +8Vdc for circuit power. Using a low-dropout regulator the
voltage is regulated to 5 VDC for logic power.
3
VersaCare™ Bed Service Manual (MAN333 REV 2) Page 3 - 9
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