Page 13
4.4.2 Internal RAM Protocol.
The data protocols available for internal RAM storage are 16bit little endian or big endian only.
Engineering unit conversion should be performed on the host PC once acquired data has been
dumped to the PC.
4.4.3 Internal RAM Data Rate.
The rate at which the data is acquired into Internal RAM is determined by the rate user command,
and the following values are available (Hz) – 1, 2, 5, 10, 25, 50, 100, 312, 500, 625, 750, 1000.
As with other communications channels, care should be taken not to request a data delivery of
more than 20k/No. channels (ie 312Hz for a 64 channel scanner).
4.4.4 Internal RAM Dump.
Data can be dumped from internal RAM on any of the other three available communications
channels. The format of the data dump is designed to be (almost) the same as if data was being
streamed out of that communications channel. So for RS232 & TCP the format of data is the same
as the 16bit LE or BE protocol formats detailed in sections 4.1.3 & 4.2.3 above (ie. Channel data
preceded by a 3 byte header (0x00, 0xFF, 0x00). For CAN the format of the data is dependant on
the selected CAN message type (single message or multiple message IDs) as detailed in section
4.3.3 above.
In addition to the above, an internal RAM dump sends a 9 (or 6) byte header, which is sent as soon
as the ‘Start Internal RAM Dump’ user command has been received by the microDAQ. This header
has the following format (note the first three bytes are not sent if the comms channel used for the
dump is CAN).
Data Byte Content
8
Total size of data
dump (in bytes)
7
6
5
4 Blocks per op
3 Number of channels
2* 0x00
1* 0xFF
0* 0x00
Figure 4.6, Data structure of Internal RAM dump header packet
(bytes marked * are not sent when dumping via CAN comms)
‘Blocks per op’ details the number of cycles of ‘n’ channels that are sent in one transmission
packet – this is dependant on the number of channels being acquired (byte 3 in header above) and
is irrelevant for CAN (always set to 1). After each packet is sent, the microDAQ waits for a
handshake to confirm that the packet of data has been received at the host PC end. The dump
handshake user command should be sent by the host PC to facilitate this (Note to avoid deadlock,
the microDAQ will wait for a maximum 10 seconds for the handshake before auto sending the next
packet). A handshake is also expected after the header packet has been sent by the microDAQ.
To Next Page
Loading...
General