HP 8560A, Service Manual

Page: 278 / 450

Note Since U512 pin 2 is at a virtual ground (currents are being summed at this
node), voltage levels at this point are difficult to interpret.
Ramp Counter
See function block D of A3 Interface Assembly Schematic Diagram (sheet 2 of 6).
The ramp counter is used for non-zero-span sweeps and for zero-span sweep times greater
than 30 ms. The analog sweep ramp is compared to the digital ramp counter. When the
analog sweep ramp exceeds the DAC output generated for that ramp counter setting,
toggles high, indicating the end of a bucket. The ramp counter counts
horizontal buckets. There are 600 buckets per sweep, so the ramp (bucket) counter counts
from 0 to 600. The ramp counter is incremented by
1. Press on the HP 8560A and set the controls as follows:
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DETECTOR MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAMPLE
2. For sweep times between 100 ms and 60 s, HODD pin 3) is a square wave with a
period defined by (2 x sweep For example, for a 6 s sweep time, HODD has a
period of 20 ms. The ramp (bucket) counter will be odd every other bucket.
Section 7-25