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Original question:

SN74HC595: How to cascade two SN74HC595?

SN74HC595: when two part SN74HC595 cascade connection, the secord part has some randomly error in some bit

Robin Liu
Intellectual 1720 points
Part Number: SN74HC595

Hi team,

My customer use two part SN74HC595 to drive 16-bit output, but the second part output always has some error. it seems randomly.

the schematic is as below.

the customer has do some probe, please refer to the below picture

1) green is U4 pin-3(QD);

2)red is RCLK;

3)blue is SRCLK;

4) yellow is DATA in U3 SER;

the only error bit of the U4 pin3 is the blue arrow indicated one. U4 pin3 is the 5th bit of 16bit serial sequence;

  • 0
    TI__Genius 16725 points

    Hi,

    The SRCLR pin is never used to clear out the internal shift registers to a known state. I am assuming you are pushing all these bits out before reading out the device.

    Its hard to read your scope shots but what frequency are you operating the SRCLK at? How much do you wait before using the RCLK?

    I can't tell what the 5th bit of the 16 pin sequence is supposed to be. Is the error the glitch to a LOW before going back high where your blue arrow points?

    Can you zoom into where the error occurs, and show the SRCLK and RCLK at that time?

    Is the glitch only happening on that single pin? If so, have you tried replacing the device?

    There is a lot happening in this device, I will need more answers before I can start to figure out whats wrong.

    Thanks!

    -Karan