HP 85662A, Troubleshooting And Repair Manual

Page: 182 / 594

Line Generator, Circuit Description
Line Generator receives a series of digital X and Y display positions, converts them
to analog values, and connects them with straight lines. This process, called line generation,
is similar to that of dot-to-dot drawing on paper. (See Figure 1.) Two independent line
generators are required: one for the X series of values and one for the Y series. For each line
there is a setup period following by a drawing period. During the setup period the display is
blanked by
Intensity Control.
‘2
l
3
‘ 4
WHEN CONNECTED BECOMES
BLANK
S E T U P P E R I O D
D R A W I N G P E R I O D
Figure 1. Line Generation Process
Each of the line generators consists of a register, a digital-to-analog converter (DAC), a
summing amplifier, a sample and hold circuit, an integrator, and a filter. The X or Y register
receives the next display point from the Digital Storage Bus. The DAC converts this number
to a current. The summing amplifier then computes a position change AX = “next
“present X.” During the setup time for the next line, AX and AY are sampled by the Sample
and Hold circuit. At the end of the setup time and during the drawing time, AX and AY are
held for constant input to the Integrator. During the drawing time, the Integrator output
changes linearly from X to X + AX and from Y to Y + AY. This is done by integrating AX
1