What does pin 9 do on this shift register?

Sorry for this newbie question, but I don't understand if I need to do anythign with pin 9 "G":

http://www.ti.com/lit/ds/symlink/tpic6b595.pdf

Here is what it says in the datasheet:
When output
enable (G) is held high, all data in the output
buffers is held low and all drain outputs are off.
When G is held low, data from the storage register
is transparent to the output buffers.

So does that mean I want G to be connected to ground if I'm using it in this sort of configuration:
http://arduino.cc/en/Tutorial/ShiftOut

I'm guessing G is the same as OE (Output Enable) on these other 595s?

"Truth table" material?

I don't know, I'm just trying to get these LEDs to light up.

Yes, it's an enable and outputs are active when G is low.

JR

Mbira said:

Sorry for this newbie question, but I don't understand if I need to do anythign with pin 9 "G":

http://www.ti.com/lit/ds/symlink/tpic6b595.pdf

Here is what it says in the datasheet:
When output
enable (G) is held high, all data in the output
buffers is held low and all drain outputs are off.
When G is held low, data from the storage register
is transparent to the output buffers.

Click to expand...

The data sheet description is wordy but entirely accurate.

When G is pulled high, the input shift register and storage register are ignored and the drains are off. That means that an external pull-up pulls the drain high. If you have the anode of an LED connected to the supply (through a current-limit resistor) and the cathode connected to one of the drains, the LED will be OFF because the drain will float.

When G is pulled low, each drain output will go to the state determined by the contents of the storage register (the second column of flip-flops in the schematic). If a bit is low, the output MOSFET is off so the drain floats. If a bit is high, the MOSFET is turned on and pulls the drain to ground. In that case, your LED turns on.

For LED driver operation, it's probably fine to tie G low active all the time. If I was using it to control relays or something else, I'd control it from my micro and make sure that I don't enable the outputs until something valid is in the storage register.

It's probably best to operate the shift register as follows: keep RCLK low while shifting new bits into the shift register (first column of flip-flops) on SER_IN using SRCK. Once all bits are shifted in, a rising edge on RCLK transfers the contents of the shift register to the storage register, updating the output.

-a

Thanks guys!