SN74HC594: Output state when /SRCLR & /RCLR are low

Zhou Fang67

Expert 4250 points

Part Number: SN74HC594
Other Parts Discussed in Thread: SN74HC595,

Hi Expert,

If /SRCLR & /RCLR are pull low, what is the output state? Is it high impedance or high or low?

Thanks.

Zhou

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 96792 points

Hi Zhou,
Can you please direct me to where that image came from? There isn't an "RCLR" pin on the SN74HC595, and all the timing diagrams in our datasheets do not have that line.

0 Zhou Fang67 over 6 years ago in reply to Emrys Maier

TI__Expert 4250 points

Hi Maier,

Sorry for error. The P/N is SN74HC594.

Thanks.

0 Emrys Maier over 6 years ago in reply to Zhou Fang67

TI__Guru* 96792 points

Thank you for the clarification!

The block diagram for the '594 will tell you what will happen:

In the above image (pg 1 of the datasheet), you can see that the RCLR\ line (highlighted in yellow) directly connects to the output registers' reset pins. This means that when RCLR\ is LOW, those registers will output LOW.

The SRCLR\ pin directly connects to the reset line for the shift registers' reset pins. This means that when SRCLR\ is LOW, those registers will output LOW.

So, if you make both SRCLR\ and RCLR\ LOW, then the device will output LOW on all outputs, and all internal registers will be reset to LOW.

0 Zhou Fang67 over 6 years ago in reply to Emrys Maier

TI__Expert 4250 points

Very clear.

Thanks.

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SN74HC594: Output state when /SRCLR & /RCLR are low