HP 85662A, Troubleshooting And Repair Manual

Page: 185 / 594

X Filter
The X Filter is a 2.5 MHz low-pass filter which smooths out transients from the X Integrator.
Y Register
and form a Y Register. When a new Y position is present on of the
Digital Storage Bus, the CHAR line is held low and positive-going edge on LDY causes
and
to be loaded with the value of These 10 bits then become the Y position
input to the Y DAC. When characters are being drawn, bits 1 through 4 of the Y Register are
changed. BO-B3 of the Digital Storage Bus carry the series of Y values representing the Y
components of the character strokes. When the next Y value is present on BO-B3, the CHAR
line is held high and a positive-going edge on LDCHAR causes to be loaded with the new
values for bits 1 through 4 of the Y position.
Y DAC, Y Summing Amplifier, Y Sample and Hold, Y Integrator,
and Y Filter
The Y DAC, Y Summing Amplifier, Y Sample and Hold, Y Integrator, and Y Filter operate
in a manner identical to that of the corresponding X Line Generator circuits.
Expand Register
U14 is a 2-bit Expand Register which provides scale and origin-shift information to the X and
Y Line Generators. When a new expand value is present on B6 and B8 of the Digital Storage
Bus, a positive-going edge on LDEXP causes
to be loaded with the value of B6 and B8.
A high on B6 will cause a scale increase of 13 percent over normal (the graticule is drawn
at normal scale) and an origin shift of 13.6 percent of normal scale.
and Q17 provide
buffering from the TTL signals to the analog circuits.
Reference
U13 provides the reference voltage to the X and Y The magnitude of the reference
voltage is proportional to the scale of the Line Generator output. For normal scale the
reference voltage is nominally -5.12 V. For the three expanded scales, the reference may be
-5.8 V, -7.9 V, or -8.6 V.
Y Offset
The Y Offset circuit supplies a signal to the Y Summing Amplifier such that the output of the
Y Line Generator will be 0 V when the Y Register contains all zeroes and no origin shift is
present. YOS potentiometer R43 is used to make the adjustment.
4