Keithley 2400 Service Manual

ROM
U15,
U16
Microprocessor
U3
GPIB
Reset
Serial
Interface
U4
U6, U13
U20
To Display
Board Controller
Trigger
Trigger
U23
Digital
I/O
U7
Digital
I/O
A/D
Control/Data
A/D
Interface
U9, U25
Voltage Source
Control
16.78MHz
E PROM
2
U17
RS-232
Interface
IEEE-488
Interface
RAM
U12,
U14
Fi
gure 4-4
Digital board block diagram
4-9 Model 2400 Service Manual
Troubleshooting
2400-902-01 (G - Feb 2006)
DS901 is the VFD (vacuum fluorescent display) module, which can display up to 49 charac-
ters. Each character is organized as a 5 × 7 matrix of dots or pixels and includes a long under-
bar segment to act as a cursor.
The display uses a common multiplexing scheme with each character refreshed in sequence.
U903 and U904 are the grid drivers, and U901 and U905 are the dot drivers. Note that dot
driver and grid driver data is serially transmitted from the microcontroller (PD3 and PC1).
The VFD requires both +60VDC and 5VAC for the filaments. These VFD voltages are supplied
by U625, which is located on the digital board.
The front panel keys (S901-S931) are organized into a row-column matrix to minimize the
number of microcontroller peripheral lines required to read the keyboard. A key is read by
strobing the columns and reading all rows for each strobed column. Key down data is inter
-
preted by the display microcontroller and sent back to the main microprocessor using propri-
etary encoding schemes.

Keithley 2400 Specifications

General

Model	2400
Category	SourceMeter
Voltage Source Range	±200 V
Power Output	20 W
Voltage Measurement Resolution	100 nV
Current Measurement Resolution	10 pA
Resolution	5.5 digits
Interfaces	GPIB, RS-232
Current Source Range	±1A
Current Measurement Range	±1A
Resistance Measurement Range	2 Ω to 200 MΩ
Display	Vacuum Fluorescent Display