Is it necessary to add a π-type filter circuit for serial communication? If the board is small and the space is limited, this must be considered.

QWE4562009

Is it necessary to add a π-type filter circuit for serial communication? If the board is small and the space is limited, this must be considered. [Copy link]

Is it necessary to add a π-type filter circuit for serial communication? If the board is small and the space is limited, this must be considered.

dcexpert

The serial port is a low-speed device. Unless there is large interference in the system or there are EMC requirements, it is not necessary.

QWE4562009

dcexpert posted on 2021-7-3 19:07 The serial port is a low-speed device. Unless there is a large interference in the system or there are requirements for EMC, it is not necessary.

If you want to add resistance and capacitance, how do you calculate the value?

dcexpert

QWE4562009 posted on 2021-7-5 15:40 If you want to add resistance and capacitance, how do you calculate the value? Moderator

It is generally not necessary, but adding it can make the waveform change less steep.

The hardware generally samples the serial port data three times, and the data bit width can be calculated based on the baud rate. After adding RC, it must be wide enough to avoid bit errors.

QWE4562009

dcexpert posted on 2021-7-5 17:30 It is generally not necessary. Adding it can make the waveform change less steep. For serial port data, the hardware generally samples three...

If the baud rate is 9600b/S, then the period is 1/9600≈104us, and the time constant of the π filter is RC=100*100*10^-12=10^-8S=0.01uS? Is this the calculation?

dcexpert

QWE4562009 posted on 2021-7-5 18:38 If the baud rate is 9600b/S, then the period is 1/9600≈104us, and the time constant of the π filter RC=100*100*10^-12=10^-8S ...

For serial communication, the requirements are not so strict. The baud rate is allowed to have a 2% error, as long as it is kept within this range.

damiaa

Serial communication sampling generally samples data 4, 8, or 16 times (digital filtering) to determine whether a bit is correct.

So the hardware filtering proposed by the OP is actually redundant. Almost no one uses it. Especially on a board. It is even more redundant.

QWE4562009

damiaa posted on 2021-7-7 08:49 Serial communication sampling is generally 4, 8, 16 times sampling data (digital filtering) to determine whether a bit is correct. So the original poster's hardware filtering is actually...

Just a direct connection?

damiaa

QWE4562009 posted on 2021-7-7 11:28 Is it a direct connection?