BC Biomedical DA-2006, Service Manual, Page: 143 / 171

B 4
MICROCONTROLLER
The microcontroller, U3, is a 16 bit central processing unit with built in peripherals. The
microcontroller utilizes a 16 bit data path. The microcontroller contains flash programmable
EEPROM, RAM asynchronous serial communications interfaces, serial peripheral
interfaces, etc. An external crystal is used to set the operational frequency at 24MHz.
Watchdog functions are built into the chip.
PRINTER PORT
The printer port consists of an 8 bit data bus driven from the microprocessor as well as 8
I/O control signals. U4, U5, U7 and U9 are used to decode the Address/Data bus and
provide the chip select signals for the printer port data latch. The control signals are used
to read the status of the printer as well as control the data flow to the printer. The filters L2
through L23 on the power supply board are used to provide electrostatic discharge
protection and noise filtering to the printer I/O signals.
SERIAL PORT
The serial port is used to communicate with a host PC. The port is fixed at 115,200 Baud,
8 Data Bits, 1 Stop bit, No parity. U1 on the microprocessor board is used to generate the
RS-232 voltage levels. L6, L8 and L11 on the power supply board are used to provide
electrostatic discharge protection and noise filtering to the serial port signals. R4, R6, and
R8 on the power supply board are used to provide short circuit protection to the serial port
signals. The port is configured for a direct to PC connection, a null modem is not needed.