HG1120 Installation and Interface Manual
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aerospace.honeywell.com/HG1120
11
Table 10. Asynchronous Inertial Message (0x0D Data Format)
POSITION
PARAMETER
LENGTH
(BYTES)
LSB WEIGHT
UNITS OR CONTENTS
1
IMU Address
1
N/A
Constant 0x0E
2
Message ID
1
N/A
Constant 0x0D
3-13
Control Data
22
N/A
Contents same as Message 0x0C
Positions 3-13.
14
Delta Angle X
4
2
-33
radians/LSB
or equivalently,
radians/second/Hz/LSB
15
Delta Angle Y
4
2
-33
16
Delta Angle Z
4
2
-33
17
Delta Velocity X
4
2
-27
0.3048 meters/sec/LSB
or equivalently,
0.3048 meters/sec
2
/Hz/LSB
18
Delta Velocity Y
4
2
-27
19
Delta Velocity Z
4
2
-27
20
Checksum
Sum of all message data (positions
1-19 of this table), taken as 16 bit
words, and summed without regard for
rollover.
2
N/A
// this pseudo code illustrates the
checksum algorithm
u16sum = 0;
for (i=0; i<24; i++) // (50-2)/2=24
{ = u16_msg_array[i]; }
Checksum = u16_msg_array[24];
if (Checksum != u16sum) {checksum
error}
Total
50
SPI Protocol
The SPI 1800/300 Hz data protocol is as specified in Table 10 – SPI Control Message and
Table 11 – Inertial Message.
The SPI 600/100 Hz data protocol is as specified in Table 12 – Control Message Format and
Table 13 – SPI Inertial Message.
These messages are identical in content to the asynchronous HG1120 Control/Inertial messages
except that Position 0 will be added and contain a 1 byte field containing the number of bytes of
data (not including spare bytes) in the message.
The SPI clock frequency must be at least 2 MHz or no faster than 9 Mhz.
The SPI clock polarity and phase are set to one (1).
SPI data order is MSB first.
A 4-wire SPI implementation is used.
The DATA_RDY signal must be used to synchronize your application to the data being produced to
ensure a consistent data set. The DATA_RDY signal must trigger an SPI fetch, and the clock rate
must be fast enough to fetch an entire message within the Control data rate (either 1800 or 600 Hz).
The SPI_SS signal should be set, then the application should clock 408 (51*8) SPI bits before
resetting the SPI_SS signal.
The External SPI device will be coming in asynchronous to the Control/Inertial message sequence.
Each SPI message in the Control/Inertial set will be a constant length. The Control message will have
spare bytes at the end, NOT included in the checksum, to match the length of the Inertial Message.
