circuit. The multiplexed a/d converter, driven by the clock A input
(23-kHz clock from CCA A7), selects front panel CLARIFIER, MGC, and
SWEEP/STEP RATE control analog inputs, and converts these into pro-
portional binary output values. The clarifier and mgc binary data
are immediately transferred to respective output registers, while the
binary sweep/step rate data are applied to a divide-by-N counter for
frequency division control. The variable counter circuit responds to
this input by dividing the clock B input (2.9 kHz from CCA A7) by N
to provide the 90-Hz/N and 1.41 Hz/N outputs. These outputs are trans-
ferred to respective sweep rate and step rate output. registers.
The A-quad-B circuits on CCA A3 convert the dual phase output of
the MANUAL TUNING optical encoder into manual tuning rate and direc-
tion data understood by the microprocessor. The resulting manual
tuning data are applied to its output register. The microprocessor
accesses data by selecting the appropriate register, using output port
7 (1-of-4 code). Data from the selected register are transferred to
the microprocessor via input. port 2. Table 5-5 shows output port 7
codes and the corresponding register selection.
g. Multiplexed A/D Converter. The. multiplexed a/d converter cir-
cuits select one of three front panel analog control inputs, convert
this input into equivalent binary data, then store these data in the
appropriate output register (see figure FO-10 and FO-11). The multi-
plexed a/d converter consists of three basic circuit. elements which
sequentially select front panel CLARIFIER, MGC, and SWEEP/STEP RATE
inputs for conversion and storage. These three elements are the a/d
controller-timer, a/d multiplexer, and a/d converter.
(1) A/D controller-timer. The a/d controller-timer selects a/d
converter input and output data, and controls the data transfer and
data conversion phases of operation. The following sequenced opera-
tions are performed by these circuits (see figure 5-9).
(a) Timing sequence 1. At the end of a previous a/d conver-
sion operation, the start/stop gate U14B and U7D is driven low to stop
the a/d converter and enable JK flip-flops U13A, U13B, and U6B with
low reset inputs. Flip-flop U6B is set by the first clock A pulse in-
put since its JK input is held high by the Q (pin 2) output of reset
(b) Timing sequence 2. The resulting high Q output (pin 1)
of U6B (one clock period length) loads the binary output of the
a/d converter into the selected register.
(c) Timinq sequence 3. During the next CLOCK A input pulse,
the high output of U6B causes U13B to set.
(d) Timing sequence 4. During the next CLOCK A interval, U13A
is set in response to the high J and low K input from U13B. The
resulting high Q output of U13A15 resets U16, and drives the output of
gate stop/start U14B and U7D high via gate U22. This high immediately
resets all three flip-flops and enables the clock input to the counter
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