Display Board Circuit Theory - Keithley 2425 Service Manual

4-12 Troubleshooting
Figure 4-5
Digital circuitry block diagram
Reset
2
E PROM
U17
A/D
A/D Interface
Control/Data
U9, U25
Voltage Source
Control

Display board circuit theory

Display board components are shown in the digital circuitry block diagram in Figure 4-5.
U902 is the display microcontroller that controls the VFD (vacuum fluorescent display)
and interprets key data. The microcontroller has four peripheral I/O ports that are used for
the various control and read functions.
Display data is serially transmitted to the microcontroller from the digital board via the
TXB line to the microcontroller PD0 terminal. In a similar manner, key data is serially
ROM
U15, U16 U12, U14
Microprocessor
U3
Model 2425 Service Manual
RAM
Serial
Interface
U4
GPIB
U6, U13
U20
Board Controller
16.78MHz
Trigger
U23
Digital I/O
RS-232
Interface
IEEE-488
Interface
To Display
Trigger
Digital
I/O
U7