picocom -b 115200 - Why do you need to specify the baudrate?

Question

I have an intel galileo board and if I try to connect to it from my laptop with:

picocom /dev/ttyUSB0

I get just akward characters like:

Terminal ready � J�)���!���#���)���!�)���!�)���!�)!!V�1��)����� J�)����� J�)�#�!�)���!�)!�Y]( V��K ��(!�Y])���!�

But if I give this additional argument -b 115200, everything is working fine.

picocom /dev/ttyUSB0 -b 115200

1. I researched that -b stands for baudrate and the number of characters transmitted per second. Is this right? 115200 per second? So many?

2. Why would you need to specify this? What in detail is working differently if we specify -b 115200?

Solution

Baud rate is bits per second, not bytes. Typically you will have more bits than just from the data bytes (8 bits) since data are sent with some overhead (framing). See for example the MathWorks discussion.

picocom is a terminal emulator, and needs to know the speed at which the device should work, because it can only ask its local side of the communication line about the speed - this has to match the remote side.

Comments

[wurtel]

Actually, more precisely baud rate is the number of symbols transferred per second. With serial lines the symbol can be either a 1 or a 0, so here it's the same as bits per second. However, some transmission channels can transfer e.g. 16 or 256 bits per symbol, with corresponding factor in bit rate compared to baud rate.