METRON QA-45, Руководство пользователя и обслуживания, Страница: 51 / 74

time reference for the processor. The frequency on TP7 is the
crystal frequency/4 (2 MHz).
U9 is an EPROM that stores the processor's program. The circuit
can store 128 Kbytes of program data. IC16 is a RAM circuit
used for storage of measurement data. Together with the LCD
display, these circuits are connected directly to the micropro-
cessor's bus. IC15 is a PAL that sends chip-select signals to the
EPROM, RAM and LCD display. The PAL circuit is in the
base, and can be replaced if the program is updated. IC7 is a se-
rial EEPROM that stores calibration data. Data is transferred
via the processor's I/O ports.
The A/D converter in the processor is used to monitor the battery
voltage. The voltage is divided by R12 and R13, and fed into
the A/D converter via port E0. The Vref. voltage from IC12
(Diagram 1) is used as the reference for the A/D (VRH).
7.3 Sensor Board
(Refer to QA-45 Sensor Board Component Location Diagram and
Schematic Diagrams 4-6)
1. Serial Interface (Schematic Diagram 4). Signal transfer be-
tween the processor board and the sensor board is in digital se-
ries form. IC108 is a serial-to-parallel converter that sends data
to the signal M UX ICl14. IC112 reads parallel data from the
switches used for operation. The data format is adapted to the
microprocessor's SPI interface, and clocked by the SCK clock
from the processor. The A/D converter IC104 (Diagram 3) has
its own serial interface connected to the SPI lines.
2. Switches For Operation (Schematic Diagram 4).
The front panel on the QA-45 has 5 push buttons and 2 sliding
controls for operation. The push buttons SW101 - SW105 are
soft keys to which different functions are assigned by the soft-
ware. The switches are read from the processor via ICl12.
SW108 is an On/Off switch that breaks the battery voltage (see
Diagram 2). SW106 (Diagram 6) sets the input attenuation by
selecting different resistor values. The switch also has a digital
connection (HI_LO and PACED signal) so that the micropro-
cessor can read the switch position.
3. Stimulus Output (Schematic Diagram 4). IClll amplifies the
stimulus signal from the processor board, and sends this differ-
entially to the pads. R141 is connected to the range selector
SW106, which provides different amplification for pacer stimuli
and defibrillation stimuli.
4. Scope Output (Schematic Diagram 5). Scope output is fed with
a signal from IC114, which is an analogue MUX. The signal
can be selected digitally from 4 sources; the scope signal from
the input amplifier for the defibrillator pads, or 3 versions (lev-
3