BMD101 Product Brief (Preliminary) 2012

NeuroSky BMD101 Product Brief Rev 0.9.2

NeuroSky Confidential

Page 10

Data Payload Format

The Data Payload itself consists of a continuous series of DataRows. Parsing a Data Payload involves

parsing each DataRow until all the bytes of the Data Payload have been parsed.

A DataRow consists of bytes in the following format:

Figure 4. DataRow Format

The DataRow may begin with zero or more [EXCODE] (extended code) bytes, which are bytes with the

value 0x55. The number of EXCODE bytes indicates the Extended Code Level. The Extended Code Level,

in turn, is used in conjunction with the [CODE] byte to determine what type of data this DataRow

contains.

The [CODE] byte indicates the type of data encoded in the DataRow. For example, a [CODE] of 0x03

indicates that the DataRow contains a heart rate value. For a list of defined [CODE] meanings, see the

"[CODE] Definitions Table" below. Note that the meaning of the [CODE] is dependent on the Extended

Code Level. Also note that the [EXCODE] byte of 0x55 will never be used as a [CODE] (nor will the [SYNC]

byte of 0xAA).

If the [CODE] byte is between 0x00 and 0x7F, then there is no [LENGTH] byte, and the [DATA] byte

immediately after the [CODE] is the 1-byte [DATA] value and the end of the DataRow.

If, however, the [CODE] byte is between 0x80 and 0xFF, then it is followed by a [LENGTH] byte indicating

the number of bytes of [DATA...]. These higher [CODE]s are used for returning arrays of values, values

that cannot fit in a single byte, or values that need a varying number of bytes to represent.

The format is defined in this way so that any properly implemented parser will not break in the future if

new [CODE]s representing arbitrarily long [DATA...] values are added (they simply ignore unrecognized

[CODE]s, but do not break in parsing), the order of [CODE]s is rearranged in the Packet, or if some

[CODE]s are not always transmitted in every Packet.