Agilent Technologies 34970A, Service Manual, Page: 155 / 273

Totalizer
Components in this discussion are located on the A1 circuit assembly
(34907-66501). The schematics are included in Chapter 8 starting on
page 261.
A simplified block diagram of the totalizer input is shown below.
The totalizer counts signals connected to the COUNT+ and COUNT–
inputs. Two op-amps, U108A and U108B, are used for input signal
conditioning. Comparator U109 determines the signal trigger levels
based upon the setting of the jumper at P102. With the P102 jumper
in the TTL position, the totalizer counts pulses with TTL trigger
levels. With the jumper at P102 in the AC position the trigger level
is at zero.
The GATE and GATE* input signals control when counting occurs.
If no signal is connected, the totalizer counts any changing signal on
the inputs. A TTL low on the GATE input or a TTL high on GATE*
input will halt counting.
Count edge selection is controlled from a U101 port bit (P0.6) through
the exclusive OR gate U111. When the P0.6 signal is low, the count
increments on the rising edge of the input signal. When the P0.6 signal
is high, the count increments on the falling edge of the input signal.
Module Reference
5
Chapter 5 Theory of Operation
Multifunction Module
153