Electrical/Control Considerations
DSX™ System Service Manual 8-3
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The following components are included in the control of the module:
MICROPROCESSOR: Provides overall operation/control of this module. The operation of
the incubation module is based around the Hitachi H8/338 single-chip microcomputer, which
provides 48Kbytes of ROM (program/data space) and 2Kbytes of RAM. The H8/338 has the
following internal peripheral capabilities:
9 ports, providing 58 I/O and 8 Input lines
Two 8-bit timers (TMR0, TMR1)
One 16-bit free-running counter (FRC)
Two digital to analog channels (DA0, DA1), with 8-bit resolution
Six analog to digital channels (AN0 through AN5), with 8-bit resolution
Two serial communications channels (COM0, COM1)
Two pulse width modulation channels (PWM0, PWM1)
RS-232 C INTERFACE: Provides serial communications between the incubation module
and the controller. Commands and test data are transferred between the microprocessor and
the external PC controller via a serial RS-232 interface. Five-volt only interface drivers and
receivers are used between the COM0 serial communications channel on the H8 and the
interface connector to provide proper RS-232 signal levels to the controller. The interface IC
used is the MAX232CD IC, which contains 2 drivers and 2 receivers in a single package. The
IC uses +5 volts to produce the required drive voltages using 4 external capacitors. The three
interface signals used are TD, RD, and DSR. Since the Incubator Module is configured as a
DCE device, TD is an input to the IM and RD and DSR are outputs from the Incubator
Module.
STEPPER MOTOR DRIVER/ PLATE MOTOR: Used for plate positioning control. The
test plate is positioned within the Incubator Module by a single stepper motor. The stepper
motor is powered by +12 volts from the external supply, and is controlled by the
microcomputer through an Allegro UDN2916B PWM motor driver IC. The driver allows the
motor to be driven at current levels of 1/3, 2/3, and full value. This allows control of the
torque and power consumption of the motor. The motor is driven in the constant torque half
stepping mode utilizing the current control capability of the UDN2916B driver.
POWER SUPPLY/ DC-DC CONVERTER/VOLTAGE GENERATION: DC voltages of
+5 and +12 volts are provided to the Incubator Module from an external power supply. The
+5 volt supply is used to provide Vcc for the digital logic, and the +12 volts is used to power
the stepper motors.
HEATER DRIVERS/ HEATER PADS/ TEMPERATURE SENSORS: The foil heater
pads used to maintain the elevated temperature of a heated test plate are controlled using the
PWM0 and PWM1 outputs of the microprocessor. The PWM0 and PWM1 outputs are
connected to power transistors that directly drive the two heaters. The duty cycle of the
PWM’s are varied to control the amount of heat generated by the heaters.
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