Hill-Rom Isolette C2000 - Microcontroller; Expansion Devices

Theory of Operation
Chapter 3: Theory of Operation
Microcontroller
The microcontroller is a PIC 16C73, used for signal processing and control of
all signals on the sensor module. The device has three external ports,
configurable as inputs, outputs, etc. The microcontroller operates from a
precise time base of crystal Y1, operating at 4 MHz. The instruction cycle time
of the PIC controller is 4 of that, namely at 1 MHz or 1 microsecond.
To ensure a clean power-up, U10 provides a fixed power-up reset to the
microcontroller. In addition, this integrated circuit generates a rest in the event
the D+5 falls below a predetermined threshold (brownout condition).
The reset line of the microcontroller, SMRES, is also available to the main
controller if the main controller determines that the sensor module requires
reset intervention.
The PIC device is operating with an internal watchdog timer device which
asserts SMRES in the event the program execution is operating outside normal
conditions.
Expansion Devices
The digital multiplexer, U3, is employed to allow additional digital signals for
processor control. It is a dual, 4-to-1 multiplexer, which allows the
microcontroller to use two ports for 8 bits of information. Control of U18 is
provided by signals DVSELO and DVSELI.
Buffered line drivers U13A/B and U14A are used for signals that are going
off-board, namely SMDATA, SCDATA and SCCLK. The SMDATA line is used.
as a bi-directional line, which can be changed from input or output “on-the-fly”
for data communication to the main controller. The SCDATA is similar, with
connection to the scale at connector J3. SCCLK is the buffered clock line used
for scale communications.
Buffer U14B provides an inversion for TMISEL, producing TM2SEL, which
alternately enables/disables temperature multiplexers.
Isolette® Infant Incubator Service Manual (man223rf) ' Page 3-15