Keithley 708B Reference Manual page 158

Models 707B and 708B Switching Matrix Reference Manual
System
Communication
Description of the crosspoint display components
The front panel of the Model 707B is composed of two main display components: a vacuum
fluorescent display (VFD) and a 12 x 12 LED matrix display, called the crosspoint display, that shows
the relay status for each of the slots.
The block diagram shows only the matrix display. Its constituent components are described below.
Microcontroller
The microcontroller receives commands from the main controller and updates the row and column
labels. It also generates the pulse-width modulated (PWM) signals for operating the 12 x 12 LED
matrix.
Row and column labels
The row and column labels are updated by writing to the devices serially. They handle their own
brightness and refresh controls, alleviating the main microcontroller from performing these tasks. As a
result, these are only updated when the data changes and a command from the instrument is issued
to update the label.
707B-901-01 Rev. A / August 2010
Figure 76: Model 707B crosspoint display block diagram
Communication
Microcontroller
Matrix Data
PWM Signals
Shut
Off
Rrefresh
Watchdog
Serial
Self-refreshing
5x7 dot character displays
Column LED drivers
12 x 12 High intensity LED array
Section 4: Theory of operations
4-7