Teensy 2.0 as a 4mhz Crystal for TI SN76489 sound chip?

[allenhuffman]

I have a Nano hooked to the Sn76489 sound chip, along with a 4mhz crystal. I started wiring up a second one using my Teensy 2.0. I ran across code examples for Arduino that seem to say I don't need the crystal, and can using the CPU itself to generate that 4mhz timing.

Is this a thing? Possibly on Teensy 2.0? It would save me a part, if so.

 

[manitou]

This will produce a 4 mhz square wave on pin 14 of Teensy 2

pinMode(14,OUTPUT);
TCCR1A = 0x43;
TCCR1B = 0x19;
OCR1A = 1;

put it in setup()

 

[allenhuffman]

This will produce a 4 mhz square wave on pin 14 of Teensy 2

pinMode(14,OUTPUT);
TCCR1A = 0x43;
TCCR1B = 0x19;
OCR1A = 1;

put it in setup()

Thank you. Where can I find docs on TCCR1x and OCR1A? Those must be similar to PORTx and such?

 

[manitou]

find teensy mcu reference info at https://www.pjrc.com/teensy/datasheets.html
this uses timer1 in fast PWM mode, with prescaler of 1 (your nano can also generate 4mhz on its timer1 or timer2 pins)

 

[allenhuffman]

find teensy mcu reference info at https://www.pjrc.com/teensy/datasheets.html
this uses timer1 in fast PWM mode, with prescaler of 1 (your nano can also generate 4mhz on its timer1 or timer2 pins)

Excellent. I was able to get it working without an external crystal. Very cool.