Diodes in 4013 D–Type Flip–Flop Circuit?

[Chris56000]

Hi!

Just a quickie one!

Can anyone point me in the direction of a good logic reference book that explains the use of diodes with a 4013 D–Type Flip–Flop please?

I have an old Intracept Electronics N7118 Colour TV Pattern Generator which has one–half of a '4013 clocked by a 4.43361875 MHz CMOS oscillator, the Q output goes to pin 2 (enable) of a '4520 decade counter (pin 1 (CLK) is earthed – I understand the '4520 will count on the positive transitions of the "enable" pin when connected this way) – what is puzzling me is that there is a diode connected between "Q" (pin 1) of the '4013 and "Reset" on pin 4, with the anode connected to pin 4 and the cathode to the "Q" output pin 1.

Part of the reason why it doesn't make sense is because the diode anode is connected to "reset" pin 4 and cathode to the '4013 "Q" output pin 1, when I would expect the diode to be the other way round, with anode to pin 1 and cathode to "reset" pin 4!

I don't have the maker's original schematic for this four decades–old piece of gear by the way – I'm having to draw it out myself!

(This piece of gear was originally supplied in d.i.y. kit form to build yourself and nobody has the original plans, and I am given to understand from a Vintage Radio Forum Member that no circuit description was provided!)

Chris Williams

[Kim Christensen]

Part of the reason why it doesn't make sense is because the diode anode is connected to "reset" pin 4 and cathode to the '4013 "Q" output pin 1, when I would expect the diode to be the other way round, with anode to pin 1 and cathode to "reset" pin 4!

If the anode was connected to pin 1 (Q output) and cathode to "reset" pin 4 (Active high), when Q goes high, it would reset the flipflop immediately making Q go low again.
ie: Q output would only go high for the duration of the propagation delay between pin 4 (reset/clr) and Q.

We'd really have to see a full schematic to figure out what the purpose of the diode is.

[Chris56000]

. . .I am continuing with drawing it out! There are two other diodes connected to pin 4 of this '4013, one goes to pin 11 (Q1) of the '4520B decade counter section that follows on from the '4013, and I've not worked out where the third diode goes to yet – all three of these diodes have their anodes connected to pin 4 with a pull–up resistor to +Vdd, so I know I have a three–input diode "wired–AND" gate with the "reset" pin 4 connected to the gate "AND" output!

Chris Williams