Moog ACV with CANopen bus interface
7 Servo valve functions
Data logger
B99224-DV018-D-211, Rev. A, October 2018
259
7.17.5 Data memory
The data logger memory is organized as a ring buffer. After the data logger has finished a sampling task and
changed the state from 'SAMPLE' to 'READY', the sampled data are valid. The sampled data start from the
byte number <SampleStartOffset> (0x3187) until the byte 2047 and continue from byte 0 to byte
<SampleStartOffset> (0x3187) – 1.
Figure 148: Data memory organization
The number of possible samples depends on the channel configuration. The next three examples illustrate
the data logger memory management:
Example 1: Sampling three channels with mixed data types, 1, 2 and 4 bytes
In this example three channels are enabled, channels 1, 3 and 4. Each enabled channel contains a different
data type with a different length (1, 2 and 4 byte). Channel one samples a one byte parameter, channel 3 a
two byte parameter and channel 4 a four byte parameter. In every sample step 7 bytes memory are needed.
The available memory is 2048 bytes. The possible number of samples is 2048 bytes/7 bytes per sample, so
292 samples can be saved in the memory. 292 samples multiplied with 7 bytes per sample are equal
2044 bytes. So an empty rest of 4 bytes remains at the end of the ring buffer. If the parameter
<Divider> (0x3182) is set to 1 (10000 samples per second), the memory is filled in 292/10000 = 29.2 ms.
Figure 149: Data memory - mixed channel data
Example 2: Sampling one channel with a one byte parameter
In this example only one channel, channel number 3, is enabled. For every sample one byte memory is
needed. The available memory is 2048 bytes. The possible number of samples is 2048 bytes divided by
1 byte per sample, so 2048 samples can be taken. No empty rest remains at the end of the ring buffer. If the
parameter <Divider> (0x3182) is set to 1 (10000 samples per second), the memory is filled in
2048/10000 = 204.8 ms.
Byte 0
Byte 2047
<
SampleStartOffset
>
(0x3187)
i.e. Byte 77
Byte 77
Byte 76
Ring buffer memory
Last samples at time t
N
Samples at time t
1
Samples at time t
2
4 Byte
Empty
...
...
<
SampleStartOffset
>
(0x3187)
Sample of 1
st
channel
INT8 (1 Byte)
Sample of 3
rd
channel
INT16 (2 Byte)
Sample of 4
th
channel
INT32 (4 Byte)
LSB
MSB LSB
MSB
