AN2818 Freescale Semiconductor / Motorola, AN2818 Datasheet - Page 13

• Manufacturer Part Number: AN2818
• Description: Romeo2 Monitor for the MC68HC908AP64 MCU
• Manufacturer: Freescale Semiconductor / Motorola

The various fields in the messages are described below.
Preamble — the Preamble is a fixed format field that allows Romeo to detect the start of a message. The
Tango3 monitor can transmit Preambles with the correct format using the 'P' field.
ID — Each Romeo device can be assigned an 8-bit ID number. It will receive messages with only this ID.
This allows each Romeo device in an RF network to have a unique ID.
The Romeo2 monitor can construct and send any ID byte using the '1' and '0' fields.
Header — The header field is a 4-bit fixed format field. It notifies Romeo that message data is next. The
field has values '0110' or '1001'.
The Romeo2 monitor can construct and send headers using the '1' and '0' fields.
Data — Data can be any length and consists of Manchester encoded '1's and '0's. The Romeo2 monitor
can construct any data pattern required.
EOM — End of Message. This is a fixed format field that indicates the end of a message. The Tango3
monitor can transmit EOMs with the correct format using the 'E' field.
The ID, header and data fields are constructed from Manchester encoded 1's and 0's. A Manchester
encoded bit is represented by a sequence of two opposite logic levels. A '0' bit of data is encoded as
sequence '01', a '1' bit of data is encoded as sequence '10'.
using Manchester encoding.
Freescale Semiconductor
Romeo2 can also accept messages with TONE based IDs. A TONE is an
ID field consisting entirely of 1’s or 0’s. Refer to the Romeo2 data sheet for
more information.
Preamble
Preamble
Romeo2 Monitor for the MC68HC908AP64 MCU, Rev. 0
Figure 6. Basic Message Formats
ID
ID
Header
Data
NOTE
EOM
Data
Figure 7
EOM
shows the data sequence '11001'
RF Message Formats
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