MAX595 startup blips

Jon Keinath

I am trying to use a MAX595 shift register in a project I am working on. I am using the Professional Development Board. The outputs of the 595 are tied to a set of 8 LED's.
When I apply power to the system they randomly display a value until the Javelin boots up and sets the correct value. Is there a way to stop the 595 from outputting anything until the Javelin is has commanded the proper value. Displaying the value on LED's isn't the final use for this, and I don't want to be pulling in motor starters and such while the javelin is booting.

I have attached the "relevant" code that I currently use, although I don't really think it is the Javelin doing it.

CPU.writePin(dataPin, false);
CPU.writePin(clockPin, false);
CPU.writePin(latchPin, false);

and the actual command routine.

CPU.shiftOut(dataPin, clockPin, 8, CPU.SHIFT_MSB, (value << 8));
CPU.pulseOut(1, latchPin); 

I tried pulling the latch pin low with a 10k resistor, but it still does the same thing. I know about the Enable Pin on the 595, but I don't think I will be able to spare the IO pin if there is another way.

Thanks in advance
-Jon

Phil Pilgrim (PhiPi)

Try putting a pullup resistor on /OE. This will keep the outputs tristated until the system resets and the program can take over.

-Phil