Service Manual

MM-E 2072-09333-00
2-29
2-4.8 Main Microcomputer Subsystem
Refer to Figure A-1.F, Figure A-1.G.
2-4.8.1 Microcontroller U5008
The main microcomputer subsystem is built around U5008, a 16-bit microcontroller with a 2K internal
RAM, and 48KB masked ROM. U5008 has a large number of I/O ports, a serial peripheral interface
(SPI), and two serial communication interfaces (UARTs), and an internal 8/10-bit A/D converter with
8 multiplexed analog inputs.
U5008 includes an internal clock synthesizer, which uses the 38.4 kHz crystal, Y5000 or Y5002, as its
frequency reference. The internal clock frequency is 16.8 MHz (nominal).
U5008 addresses the other circuits via a 19-bit address bus, ADDR0 to ADDR18. Data is transferred
via a 16-bit bidirectional data bus, DATA0 to DATA15. The direction of data flow over the bus is
controlled by the R/W_ line, and the components that can access the data bus are selected by chip-
select (CS) lines generated by U5008.
U508 is powered by +5V from the VCC line, and by +5V provided by the regulator U6021. A
power-up controller, U5014, monitors the VCC line and provides a reset signal to restart the
microcontroller and other LORD circuits when the voltage on the VCC line rises to the normal level.
2-4.8.2 Memory Subsystem
a. Flash Memory. The flash memory, used to store the application software, comprises two 256K
units with 16-bit words, U5001 and U6035. Each unit can be separately accessed, under the
control of the FLASH1 and FLASH2 lines provided by U5008.
The VPP write protect line (inverted by Q5005) prevents accidental write access to the flash
memory.
b. RAM. The RAM includes two 512K units, U5009 and U5010. In addition to the storage of
temporary variables during program execution, the RAM is also used to store operational
parameters, and therefore its supply voltage line, VBAT, can receive +5V from the VCC supply
line, or the voltage provided by the backup battery via connector J4.
The RESET line provided by U5014 is used to prevent accidental access to the RAM during
power-up, or whenever the VCC supply voltage is not within the allowed limits.
c. EEPROM. The EEPROM, U6043, is a 32K unit used to store calibration data. Access to the
EEPROM is controlled by U5008, via an access control circuit built around U6099.
2-4.8.3 Input/Output Ports
The general-purpose I/O ports of U5008 are used to generate discrete control signals, and to monitor
various status lines provided by other circuits.
In addition to its own ports, U5008 uses a set of output ports, implemented by means of the external
latches U6068, U6069, U6070, to generate control signals that change only when the operating mode
or conditions change. The access to these ports is controlled by an I/O decoder, implemented by the
latch U6079.
2-4.8.4 Handling of Analog Signals
a. U5008 has an internal A/D converter that is used to measure analog voltages. The voltages to
measured are connected to the AN0/PADA0 to AN7/PADA7 ports, and an internal multiplexer
selects the signal to be digitized at each instant.
b. The D/A converter U1104 is used to generate the BIAS OUT power control reference for the HI
POWER module, and the oven temperature control signal for the OCXO option.