AVR-Chat

Hi Owen,

On 10/3/06, OWEN-A <oldboot@bigpond.com> wrote:
> I am trying to modifying a PIC program to get a shift register to work
> properly, toggle the clear pin on the shift register to force all outputs to
> "0" to prevent it from holding the data for too long and burning out an
> expensive solenoid.
>
> The shift register is a 74HC595 and will occasionally lock an output on for
> a long enough period to destroy a solenoid.

Clearing is a two stage operation. If you take a look at the
datasheet, you'll see that there are really two 8 bit registers, one
is a shift register, and one is the output register.. The output
register is what you see on the pins. The clear connects to the shift
portion of the register.

So to clear the register, you need to drive the clear line low for a
minimum of 20 nanosecs (this clears the shift register portion), and
then strobe the RCK line from low to high to load these zeros into the
output register. The RCK line needs to stay high for a minimum of 20
nanosecs as well.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/