8
3
10.6.3
TCM
The zener diode D5 and its associated components create a +1.2V reference. This
voltage level plus AVDD are used to power the temperature compensator if attached.
Refer to schematic 834u-070 sheet 1.
10.6.4
Reset
U4, SW1 and Q1 form the reset circuitry for the micro-controller and the display. To
reset, press SW1.
Refer to schematic 834u-070 sheet 1.
10.6.5
2.5V Reference
U2 is a precision 2.5V reference used by the micro-controller during the analog to digital
conversion.
Refer to schematic 834u-070 sheet 1.
10.6.6
Download/Normal Switch
J4 is the switch that allows the download of the instruments firmware.
Refer to schematic 834u-070 sheet 1.
10.6.7
RS-232/Display Switch and RS 232 Driver/Receiver
U17 is a digital switch that allows the micro-controller to send data to the display or to
the RS-232 port.
U16 is a RS-232 Driver Receiver. This component converts data to the RS-232 level.
Refer to schematic 834u-070 sheet 6.