Hal Communications DKB-2010, Instruction Manual, Page: 31 / 101

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Figure 4.6 Morse Clock and Decoder Waveform
The 0 output of IC-31 is connected through an inverter to the J input of the dot flip-flop. The output
from one of the remaining lines is selected by the weight control (S302), inverted, and fed to the K input.
When the counter is in the "0" state, the dot flip-flop's J input is therefore high and its K input is low.
On the first negative-going clock transition, the dot flip-flop assumes the state of its J and K inputs; that
is, it toggles to the "1" state, as shown in Figure 4.7. The DOT line, connected to the toggle input of the
dash flip-flop (pin 11 of IC-22) goes high.
Figure 4.7 Production of Dots by the Morse Character Generator
Assuming for the moment that S302 is set for normal weight, the K input of the flip-flop is driven by
decoder output 4 (pin 5). During the next three clock pulses, the flip-flop does not change states because
its J and K inputs are held low. After clock pulse 3, however, the decoder 4 output goes low, driving the flip-
flop's K input high. On the next negative-going clock transition, the flip-flop changes back to its original
state, pulling the DOT line low. The flip-flop does not revert to the set condition until the counter has
completed its cycle and a new bit has been supplied by the shift register. The dot pulse is therefore followed
by a space.
Because it is possible to select which decoder input is used to reset the dot flip-flop, the duty cycle of the
output may be varied. The duration of the dot as compared to that of the following space may be set for
any ratio from 1:7 to 3:1. Four of the six possible weight ratios are selectable by the weight switch, as
determined by the position of the jumpers on the circuit board.