Communication protocol

Serial port

Communication with the board is established through the serial port, with a 2Mbps baud rate, 8bits, no parity, one stop bit (8N1).

Message format

Messages sent to and received from the microcontrollers are byte oriented streams. All messages start with a caret sign ^ (0x5e) and end with a dollar sign $ (0x24).

Table 1. Message format
Bytes	1	n	1
	`^`	`n unsigned bytes`	`$`

An exclamation mark ! inside a message body indicates a transmission error and invalidates the whole message. The characters ^, $, ! and \ are special and must be escaped with a backslash \ followed by the two’s complement of the escaped character (they are thus encoded on two successive bytes).

Table 2. Special characters
Special character	Escaped version inside a message body
`^`	`\ 0xa2`
`$`	`\ 0xdb`
`!`	`\ 0xde`
`\`	`\ 0xa3`

All messages may embed signed or unsigned integers. They are encoded on 1, 2 or 4 bytes (depending on the message format decribred later), in big-endian format (most significative byte first).

Table 3. Integer encoding
Bytes	1	2	3	4
8 bits integer	`n`
16 bits integer	`n >> 8`	`n`
32 bits integer	`n >> 24`	`n >> 16`	`n >> 8`	`n`

Messages

ID

This message queries the softwareversion.

Table 4. ID query message
Bytes	1	1	1
	`^`	`?`	`$`

Table 5. ID reply message
Bytes	1	1	n>6 (string)	1
	`^`	`?`	`arduioX.Y`	`$`

X.Y represent the software version running on board.

GPIO direction

This message configures the given GPIO for input, with or without pullups, output or PWM.

Table 6. GPIO direction message
Bytes	1	1	1	1	1
	`^`	`d`	`n`	`direction`	`$`

n is the GPIO number, direction is an integer mapped according to the following table:

direction	input/output type
0	`input`
1	`input + pullup`
2	`digital output`
3	`~31kHz PWM output`
4	`~122Hz PWM output`
5	`~31Hz PWM output`
16	`WS28XX RGB led output`

GPIO out

This message sets the output state of a GPIO.

Table 7. GPIO out message
Bytes	1	1	1	2	1
	`^`	`o`	`n`	`v`	`$`

n is the GPIO number, v is interpreted as

a boolean for digital outputs,
the PWM duty cycle (65535 is 100%) for PWM,
the led index/color for WS28XX (see Modes of operation).

GPIO out array

This message sets the output state of the first n GPIOs.

Table 8. GPIO out message
Bytes	1	1	1..2n	1
	`^`	`O`	`v`	`$`

For each GPIO starting from 0, v is interpreted as

a boolean for digital outputs,
the PWM duty cycle (65535 is 100%),
the led index/color for WS28XX (see Modes of operation).

GPIO in

This message returns the state of a GPIOs.

Table 9. GPIO in message
Bytes	1	1	1	1
	`^`	`i`	`n`	`$`

n is the GPIO number. The reply has the following format:

Table 10. GPIO in reply
Bytes	1	1	1	2	1
	`^`	`i`	`n`	`v`	`$`

n is the GPIO number, v is the state (0 or 0xffff for digital I/Os, or the PWM duty cycle for PWM, or the led #0 color.

Analog I/O in

This message returns the state of an analog input.

Table 11. Analog in message
Bytes	1	1	1	1
	`^`	`a`	`n`	`$`

n is the I/O number. The reply has the following format:

Table 12. Analog in reply
Bytes	1	1	1	1	1
	`^`	`a`	`n`	`v`	`$`

n is the pin number, v is the analog state value.

State request

This message returns the state of all GPIOs and analog input.

Table 13. Analog in message
Bytes	1	1	1
	`^`	`s`	`$`

The reply contains two messages, with the state of digital I/O and analog pins.

Table 14. State reply
Bytes	1	1	1..n	1
	`^`	`I`	`v`	`$`
	`^`	`A`	`v`	`$`

The 'I' array is for all GPIOs, the 'A' array for analog inputs.