Command String Protocol

This is the protocol for communication between the PICAXE 28X1 and the Flight Computer

Flight Computer to Avionics Command Protocol and Strings

All command strings to the avionics set begin with the capital letter “C”. Any string coming into the serial buffer should be ignored if it does not begin with a C.

The following three numbers after the C denote the command category, exact command and following bytes. Any additional information may be included in the following variables, although these need not be specified and can be omitted. The three command string bytes after the C are, however, mandatory.

The third number after the C denotes the number of following bytes including the stop bit, which is defined as “\n”. So C121 means C120 with \n at the end.
This third number should never be 0! It takes a minimum value of 1.

Data sent from the avionics kit to the flight computer should NEVER contain a C.

B0	Notes	B1	Ex	What it means / does
1	If a C1* command is sent by the flight computer, it is expecting a response. The avionics set must respond as quickly as possible.	1	C111	The flight computer requests the string
		2	C121	The flight computer requests the time in the format hhmmss.
		3	C1320	The fPC gets an ADC reading on the channel sent to the PIC (ch. 0 in the example)
		4	C141	Ping Pong
2	A C2* command is sent by the flight computer when it is not expecting a response (except acknowledge). The avionics set should, however, be at a ready state as soon as possible after actioning the command.	1	C211	Flash LED/Light/Siren for 5s
		2	C227123000 (sets time to 12:30:00)	The flight computer wants to set the time from the attached GPS device to the avionics clock device. This should be in the format hhmmss.
		9	C291	The flight computer requests activation of the cutdown device.
3	C3* commands are reserved for camera control sequences. No other system or device should use the C3* range of commands.	1	C3121	Take picture NOW, pulsout length is the 4^th digit multiplied by 30.