Tabor 8020 - Counter Circuit; IEEE-488 Interface (Option 1)

tors Q1 through Q8 which, in turn, drive the anodes of the
appropriate LED. The sense lines S0, S1 and S2 determine
which of the button were depressed.
6-6-2. Counter Circuit
The counter circuit is employed in the model 8020 for the
purpose of controlling the accuracy of the frequency at the
output connector. The counter circuit is composed of di-
vider U10, selector U11, D flip-flop U12 and selector U13.
The counter circuit counts the number of pulses from the
VCO. The CPU then computes the relation between these
pulses to the reference clock. The result is compared to the
required accuracy. If deviation is sensed, the CPU sends
correcting data to the current generator circuit.
6-6-3. IEEE-488 Interface (option 1)
The instrument has a built in IEEE-488 interface that per-
mits remote control through a system controller.
The IEEE interface is made up of U11, (General Pur-
pose Interface Adapter), U15 and U16 interface bus driv-
ers. On the CPU side of the GPIB, data transmission is han-
dled much like any other bus transaction. The output of the
U14 is standard IEEE format and is buffered by the two
IEEE bus drivers U15 and U16. The bus divers are neces-
sary for enhancing the drive capability of the interface. Up
to 15 devices may be connected in parallel.
Theory Of Operation Model 8020
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