ADXL180
Rev. 0 | Page 21 of 56
TIME
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DATA FRAME DEFINITION
DATA FRAME TRANSMISSION FORMAT
DATA BITS
LOGIC SIGNAL
AT CONTROL
MODULE DECODER
‘0’
‘1’
DATA BITS
0
LOOP
CURRENT
I
MOD
I
IDLE
START
BIT 0
START
BIT 1
START
BIT 0
START
BIT 1
t
M
t
B
0
75
44
-0
36
Figure 17. Data Message Timing (Manchester-1, Bit Coding)
A data frame starts with two start bits. The value of these two
bits is determined by the Manchester encoding mode select bit.
See the Manchester Data Encoding section. Figure 17 shows the
basic format and timing of the data frame. A 1-bit idle time is
an implicit stop bit at the end of a data frame.
DATA FRAME CONFIGURATION OPTIONS
Figure 18 diagrams the protocol data frame construction
options. The data frame can be broken into four specific fields
as follows:
•
Start bits—two start bits are always transmitted at the start
of the data frame. These bits are used to synchronize the
center module decoder with the Manchester encoded signal.
•
Error checking—a single parity bit or a 3-bit CRC code can
be selected.
•
State vector—identifies the type of data in the data field. It
can be disabled. When it is disabled, it is not transmitted.
•
Data—the device data and sensor data can be transmitted
in either 8-bit or 10-bit mode.
Depending on the settings of the configuration register bits
(ERC, SVD, and DAT), the data frame can be from 11 bits to
18 bits in length. Figure 18 shows the formats of the available
data frames. Note that the error checking field is transmitted
first when the CRC is selected but transmitted last when parity
is selected. See Figure 18 for specific examples of full protocol
configurations.
