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.
The first two lines of the for loop,
byte upper_byte = input_bin >> 8;
byte lower_byte = input_bin & 0x00FF;
don’t really accomplish anything. The first line is bit shifting to the right 8, and then you just bitwise and it resulting in the same thing. For example, starting with input_bin:
1000 0000 0000 0000
>> 8
0000 0000 1000 0000
& 0xFF
0000 0000 1000 0000
So, every time you go through a cycle of the for loop, you’ll just start with the same values in upper_byte, and lower_byte. To sequentially output each shifted value, you’ll instead want something like:
output_value = 0b1
for i = 1 to 16:
latch(low)
shift_out(output_value)
latch(high)
output_value = output_value << 1
That is, if I interpereted correctly that you want the shift registers to output the following:
output_count, upper_shift_register, lower_shift_register
1, 00000000, 00000001
2, 00000000, 00000010
3, 00000000, 00000100
.
.
.
16, 10000000, 00000000
Note: Lemmy has a bug where it doesn’t format some symbols correctly, so the left angle bracket gets formatted as . The same issue exists for the right angle bracket, the ampersand, and I would presume others.
I think you got and and or switched, first two lines should be fine for shifting the top 8 bits down.
I think what he refers to is that you seem to do a bitwise or for the second line instead of the bitwise and.