# synchronous binary counter question

Discussion in 'General Electronics Discussion' started by Joseph K., Nov 6, 2015.

1. ### Joseph K.

3
0
Nov 6, 2015
Hi all
I'm trying to wrap my head around the midi2cv circuit from the following link:
http://musicfromouterspace.com/analogsynth_new/THE_CAVE/MIDI to CV Old Design I/midi2cv.htm

The explanation provided on the page is very good, but there is something that
I don't understand.
According to the explanation, the circuit uses a cd4520 binary counter to "count from 0 to 248".
This is where I get lost.
Of course I checked the datasheet and searched for tutorials etc. but from what I can see, the maximum number that can be counted with a 4-bit binary counter is 15. (full range: 0-15)
I can see how one could link several counters in order to increase the overall count, but how does one arrive at the exact number of 248?
I tried to figure it from the circuit schematic, but that did not make me any wiser.
Any explanation would be greatly appreciated.
Cheers!

2. ### AnalogKid

2,498
718
Jun 10, 2015
Th 4520 is a DUAL 4-bit binary counter. You string the two halves together by connecting the Q4 output of one half to the clock input of the other half to create a single 8-bit counter. Note that each 4520 on the schematic has two clocks, two Q1's, etc. From the text above the schematic (emphasis mine):

Clock Generator
Since MIDI data speed is fixed at 31.25KHz we need to grab the data at the right time so our circuit's timing is critical. We start off with a 2MHz clock module (IC1) and divide this frequency by 8 using IC3 (CD4520 dual binary counter)

ak

3. ### dorke

2,342
665
Jun 20, 2015
1.The two 4-bits counters in the 4520 are cascaded to create an
8-bit counter.
2.An 8-bit counter would count from 0 to 255.
(in binary 00000000 to 11111111)
3.To count up to any number in between these values,that value needs "to be recognized" i.e detected and cause the counter to be rest to 0.
4.In the circuit the value 247 (=248-1) in binary 11110111 (=11111000-1 ) is detected by 5 diodes that form a 5 input AND-gate.
notenly the 5 msb are detected! that is 11110xxx.
5.When the value 247 is detected (#4 above).
The circuit consisting of 2 Schmidt-trigger inverters(U7),a diode and R3-C2, create a logic "1" pulse.
This pulse connected to the counters reset pins,
resets the counter to all 0's (async reset)
-->see the Red arrows in the pic.

Tha fios agaibh, CDRIVE and Joseph K. like this.
4. ### Joseph K.

3
0
Nov 6, 2015
Exactly the explanation that I needed.
Much obliged!
Take care.

5. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
JMHO but I think it deserved a tad more. Like STELLAR!

Chris

6. ### Joseph K.

3
0
Nov 6, 2015
Hi Chris,
I agree
Hi Chris,
I completely agree, but I couldn't find the corresponding button and the selection of available smileys is not exactly top notch either.
Cheers,
Joseph

7. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
Yes, we need a "Love It!" button.

Cheers,
Chris