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Midi Clock Converter/Divider MC628




The MC628 is a converter to transform MIDI Clock [F8] messages provided by any MIDI sequencer to an analog "pulse" signal to send to Trigg/Pulse/clock inputs of analog sequencers,drumboxes, modulars.

  • Divide by N the MIDI clock (N = 1 to 255)
  • 1 gate led (optional)
  • Edition by Sysex MIDI (N & Id)
  • Keep config when off.
  • Output voltage  TTL +/- Logic
  • Power Supply +5V
  • MIDI editor/config software for PC

The cpu is a PIC16F628-20 microcontroler with a MIDI I/O interface.The software encoded in the PIC is a MIDI clock divider from 1 to 255 . The PIC receive MIDI clock messages <F8> , count them until a threshold value has been reached and if it is the case, pulse a couple of pin (RA0,RA1). Note the clock (+/-) provided by the interface is not a square (50% PW cycle) signal , but a short pulse clock around 4 or 5 ms. I do not calculate this precisely, just set it to the shortest working value with all my test devices: a Korg  SQ10, DS7 clone, the ASM1X... There is a delay time value in the code to increase the length of the pulse, but i did not leave it editable. Usualy the interface is set to deliver pulses from 1bpm ( or less)  to 96 bpm. 4, 8,16 bpm are probably the most used settings. The clock divider value is set with MIDI exclusive message, also there is no need for knobs or push buttons. An optional led give informations on the state of the interface.

Schematic & pcb
Clock outputs are J1 pin 1 for Negative Pulse and J1 pin3 for Positive Pulse. Other pins are free. The generic schematic i drawn contains a lot of  unused parts for this application ( J5,R4,R5 5) . It is possible to remove R6& R7 but the RA4 port (pin10 of the PIC) must be connected to ground. It is used for ISCP-LV programming ( see Microchip datasheet). D1,R3 are fully optional If implemented the led ligth on when a Midi Clock message or a SysEx message is received...Already etched/drilled pcb are available , see end of page.


  1. MC628 Schematic ( Gif)
  2. MC628 PCB parts side( Gif)
  3. MC628 PCB solder side( Gif)
  4. MC628 Bill of materials ( txt)

Important Notes 

  1. Crystal oscillator is 20MHz and not 4MHz .
  2. Use a PIC16F628-20.


Inside the SQ10... a MC628


Firmware for PIC16F628

It is the main piece of code, the brain of the interface. Download it into a PIC16F628 microcontoler. The file contain all Config flags of the PIC. Do not change them. It is possible to use low voltage ICSP  to burn the PIC, as the firmware was coded this way and leave free ICSP pins ( RB6,7,4). Classic method for programming PICs work also well.

Assembler source code for the MidiClock628 v1.2 

The PC Config Software
The MC628 memory is fully editable with MIDI exclusive messages.I have written a complete MC628 editor/test software for PC under Windows 9x/XP.This software is freeware and is useful only with the MC628...

Download "MC 628 config software V1.1" for PC ( 1.1Mb)

    To install the software :

        1. Unzip to any folder on your hard drive.
        2. Run the MC628_1.exe
        3. Enjoy !

It is also possible to send MIDI exclusive messages with a MIDI sequencer or any device able to do that ... Here is a file who describe sysex messages calculations to send to the MC628 to setup the MIDI clock divider (1 to 255)

Korg SQ10 and MC628
Here are pictures of the MC628 installed in a Korg SQ10 analog sequencer to make it MIDI synchronisable with any MIDI sequencers. This is an example... The MC628 can be used with many others analog sequencers or drumboxes.

Download Wiring draw of the MC628 inside a Korg SQ10

The Pulse out of the MC628 is wired to the External STEP jack input of the SQ10. The + psu is drained from the 7815 ( pin 1 -input ) on the SQ10 mainboard. ( red wire on the psu picture) .The ground is connected to jacks STEP and START/STOP jacks ground pins, by the MC628 pcb directly soldered to them. (see pictures). As it is a small pcb, there is no mechanical problems and no more hole to drill than the MIDI plug. It is the great advantage of this "upgrade" , also fully reversible and wired in less than an hour ! Now there is a minor drawback to this simple method of : To drive a Korg MS10/20 with the SQ10 in MIDI sync mode, the GATE signal must be plugged to the SQ10 External STEP Jack - this input is now an output... because the SQ10 "Multi trig " output provide now a too short pulse to drive correctly the MS10/20 envelope.



© Marc BAREILLE 2004