Top octave

Top Octave Frequency generator

An attempt to build a top octave divider. This can also be used to make any static prescaler.

Restrictions

DC Characteristics

Original MOSTEK chips require a supply voltage of ~15v (Max 16v). Input clock voltage must be between 0v and Vss -1v min. To avoid this, a TTL compatible master clock is include in schematic (Typical clock frequency is 2.00024 MHz).

Duty cycle

MOSTEK chips differs in their number of dividers and duty cycle :

• MK50240 : 50% - 13 dividers (239 to 478)
• MK50241 : 30% - 13 dividers (239 to 478)
• MK50242 : 50% - 12 dividers (239 to 451)

This emulation only generate a (almost) 50% duty cycle. Thereby, MK50241 model is not supported since the timbre will be affected.

Power consumption

Original MOSTEK chips sink 24mA@15V : 0.36w Typ. (Max 37mA@15V = 0.56W). You need 13 attiny4/13 to emulate a MK50240 (12 for a MK50242). Total power consumption for 13 ATtiny13 is about 30mA@5V (Not include clock circuitry).

TODO

• Support 30% duty cycle

Other use

The script genedivider.pl can be use to generate assembly code for any static prescaler. For example, to build a by 42 prescaler:

./genedivider.pl 42 > divide.S

If an overflow/underflow occurs you can try to adjust $loop variable:

./genedivider.pl 10000 200 > divide.S

Warning, the script do not check the generated code size.

Programming the attiny4

The ATtiny4 require a programmer that is compatible with the TPI mode (Tiny Programming Interface).

To flash one divider with avrdude, connect the attiny to the programmer as follow:

 USBASP               ATTINY
   +5v <-------------> +5v     (pin 5)
   gnd <-------------> gnd     (pin 2)
 reset <-------------> reset   (pin 6)
  MOSI <-------------> TPIDATA (pin 1)
   CLK <-------------> TPICLK  (pin 3)

then

avrdude -c usbasp -p t4 -U flash:w:437.hex

and apply fuse configuration

avrdude -c usbasp -p t4 -U BYTE0:w:0xfa:m