Serial! It's what's for breakfast

Me: I want to write a program that talks to a serial port. Reality: What is serial port? How does work?

This talk aims to fill in that reality gap. I'll cover the basics of what serial is, how it works (RTS/CTS, stop signals, buffers), and possibly go over how to write/interact with Unix serial ports (in C or walk through part of the python pyserial library. TBD).

All serial info to be based on the RS-232 protocol.

Presented at bangbangcon 2014
Talk recording: http://youtube.com/watch?v=J1CQz8XyWoo

Transcript

1. SERIAL! It's what's for breakfast lisa neigut | @niftynei Animation by Paul Lau & Roy Stanfield
2. import serial ser = serial.Serial('/dev/tty.usbserial-FTELSI2D', 9600) ser.write("some stuff") byte = ser.read()
5. serial | parallel
10. pins, wtf!
11. RX Received Data Pin 2 TX Transmitted Data Pin 3 GRD Ground Pin 5 RTS Ready to Send Pin 7 CTS Clear to Send Pin 8
12. TX / RX
14. GRD
16. frames!
17. 00100110|0|11
18. 00100110|0|11
19. #define CS5 0x00000000 /* 5 bits (pseudo) */ #define CS6 0x00000100 /* 6 bits */ #define CS7 0x00000200 /* 7 bits */ #define CS8 0x00000300 /* 8 bits */
20. 00100110|0|11
21. parity: odd, even, mark, space, none
22. 00100110|0|11
23. stop: 1, 1.5, 2
24. 8N1 5E2
25. speed!
26. baud rate
27. 9600 bps 115200 bps
28. import serial ser = serial.Serial('/dev/tty.usbserial-FTELSI2D', 9600) ser.write("some stuff") byte = ser.read()
31. <3 <3 <3
32. 33<
33. control flow!
34. RTS / CTS
35. RTS Ready to Send Pin 7 CTS Clear to Send Pin 8
36. XON 17 XOFF 18
37. but how!
38. /* * Defaults on "first" open. */ #define TTYDEF_IFLAG (BRKINT | ICRNL | IMAXBEL | IXON | IXANY) #define TTYDEF_OFLAG (OPOST | ONLCR) #define TTYDEF_LFLAG (ECHO | ICANON | ISIG | IEXTEN | ECHOE|ECHOKE|ECHOCTL) #define TTYDEF_CFLAG (CREAD | CS8 | HUPCL) #define TTYDEF_SPEED (B9600)
39. /usr/include/sys/termios.h /usr/include/sys/ttydefaults.h