OHAUS TROOPER SCALE, Руководство по обслуживанию

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2-2
CHAPTER 2 THEORY OF OPERATION
2.3.3 Microprocessor U7
The microprocessor U7 contains a built in RAM, ROM and an LCD driver. Crystal Y1 operates at a
frequency of approximately 4.00 MHz and is used to control the frequency of the microprocessor. The
microprocessor provides serial data to the LCD display as well as parameter storage to EEPROM
U11. A TTL level signal is also provided to U1 (Max 202) for RS232 communications.
2.3.4 MELSI U8
The MELSI, U8 is a digital controller used in conjunction with the A/D Converter. It provides all digital
functions required to run two independent A/D channels. The oscillator of the MELSI works with an
external crystal (Y2) which operates at a frequency of 11.0592MHz.
2.3.5 Memory Storage
The EEPROM U11 is the user memory storage device for the indicator. It contains 1024 bits of memory
and stores the calibration data and the selected units which are enabled and disabled. When the scale
is turned off, all previous settings are retained.
2.3.6 LCD Display Information
The display information for the LCD comes directly from microprocessor U7 and is decoded with it's
internal circuits. The LCD is backlit by panel BL1 and driver circuitry BL2 operated from BKLIT signal
from microprocessor U7.
2.3.7 Display ON/OFF
The unit contains an ON/OFF button. There is a power-save mode in the software. When this feature
is enabled, the scale will automatically turn off after 5 minutes after last keypad operation.
2.3.8 A/D Converter
The A/D converter takes the analog input voltage from the load cells and produces a digital output code
which represents the analog input. This is derived through U3, U4 and U5 circuitry. The SEN line is
to compensate for temperature influence. Two jumpers Jump1 and Jump 2 may short the SEN and
EXC for a four wire system.
2.3.9 Load Cell Excitation Voltage
A six (6) wire interface for the analog load cells is provided at J4 located on the PC board. Excitation
voltage for the load cells is +5 Vdc.
2.3.10 RS232 Operation
The RS232 half-duplex operation is controlled by the microcontroller U1, MAX 202. Signals
supported are RXD, TXD and GND. There is no handshake interface. The serial port may receive the
external Tare, Zero and Print command in ASCII code.
2.3 PRINTED CIRCUIT BOARD THEORY (Cont.)