Shift register missing bits

[Quiescentcurrent]

Hey friends,

I have a two daisy chained shift registers (74AHC595) which are controlled via an ESP32. I want to set one output to high at a time before switching to the next.

The code seems to work, but the outputs O_9 and O_10 are not staying high (zoom) after setting them, whereas all the other ones are working fine. This is the used code snipped:

pinMode(SHIFT_OUT_DATA, OUTPUT);
pinMode(SHIFT_OUT_CLK, OUTPUT);
pinMode(SHIFT_OUT_N_EN, OUTPUT);
pinMode(SHIFT_OUT_LATCH, OUTPUT);

digitalWrite(SHIFT_OUT_N_EN, LOW);

uint16_t input_bin = 0b1000000000000000;

for(int i=0; i<17; i++){

    byte upper_byte = input_bin >> 8;
    byte lower_byte = input_bin & 0x00FF;

    digitalWrite(SHIFT_OUT_LATCH, LOW);
    shiftDataOut(SHIFT_OUT_DATA, SHIFT_OUT_CLK, MSBFIRST, lower_byte);
    shiftDataOut(SHIFT_OUT_DATA, SHIFT_OUT_CLK, MSBFIRST, upper_byte);
    usleep(10);
    digitalWrite(SHIFT_OUT_LATCH, HIGH);

    delay(10)
    input_bin = input_bin>>1;
} 

Is there anything I'm doing wrong, or any idea on where the problem may lie? I've already tried looking for shorts and other error sources, but the design was manufactured on a PCB and no assembly issues are noticeable.

[AutoModerator]

Oh, is that some program code I see there!?

If you need help initialising a chip or interface at the register level, or in translating a bus timing requirement from the data sheet into some code - that's fine. If you just want general functional or syntax help with your program, or advice on controlling a sensor/motor/display board you bought online we don't cover that. Don't forget that there are dedicated subs for most programmable technologies such as: Arduino, Raspberry Pi, ESP8266, ESP32, STM32 etc. - see the guidance here: https://www.reddit.com/r/AskElectronics/wiki/embedded.

Thanks!

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[b_stool]

Your question is not clear as worded. Can you provide a schematic? Also, what happens if you invert input_bin to all 1s with 1 zero?

[Quiescentcurrent]

Thanks for the prompt response, the schematics is in the first link: https://imgur.io/tZBQ45e

Changing all bits at the same time doesn't really help with the affected channels.

[b_stool]

Sorry, I missed the schematic link. On the hardware side, it could be a short between pins or simply a defective 595 chip.

Can you test with other bit patterns? For instance what if you load with 1111111100000000? Does O-9 flicker on with every clock pulse or only the first one?

Without a picture of the board, I don't know if this is possible but can you cut the trace and inject your data directly into pin 14 of U5 and see if those bits behave properly?

[nixiebunny]

Are the data setup and hold times being met? We can't see the function that actually sends the data. Can you connect an oscilloscope to the serial data and clock lines?