Basic Protocol Description

This is the protocol description written by Dave Baum:

Date: Sat, 29 Aug 1998 19:10:15 -0500
To: Larry Pieniazek 
From: Dave Baum 
Subject: RE: Lego Mindstorms page

The IR protocol associated with sending a "message" to the RCX is pretty
simple.  Bit encoding is 2400 baud, NRZ, 1 start, 8 data, odd parity, 1
stop bit.  A '0' is coded as a 417us pulse of 38kHz IR, a '1' bit is 417us
of nothing.

At the packet level, all packets look like this:

0x55 0xff 0x00 D1 ~D1 D2 ~D2 ... Dn ~Dn C ~C

where D1...Dn are the message body, and C = D1 + D2 + ... Dn.

The data for sending an IR message is F7 followed by the 8 bit "message".
For example:

55 ff 00 f7 08 12 ed 09 f6

is a packet sending the message "0x12" to the RCX.


Back to RCX Internals.