Summary: Interruption
of a data packet from a Visa serial port with repeatable actions when using a
cRio 9474.
Environment:
NI-PXI-8190 Pentium 4 2.0 Ghz system 512MB RAM, Windows XP Pro
SP2, Labview 8.0.
PXI-7811R with cRio units: 3-9263’s; 9221; 9401; 9474; 9435;
9215.
2630 multiplexor, and an 8421-RS485.
Visa 3.4.1;
NI Switch 3.00.49161;
NI-Serial 1.8.1;
NI-DMM 2.5.0
This is to become a test rig for a small aircraft embedded
engine control system.
The control system
produces a multi-channel data stream to a RS 232 serial port.
We are reading this using Visa Configure and
Visa Reads.
As we are continuously
reading the data stream, we are sending signals to the control system through
the cRio devices to simulate the temperatures, pressures and speed (Rpms) of
the engine.
We are using the 9474 to
simulate the engine speed, and when the external power supply to the 9474 is
started, the data stream being read is interrupted (instead of 78 bytes packet read,
only 24 are placed into the Visa read buffer).
The property node (Bytes at Port) shows 78 bytes, the Read
asks for a byte count of 78, but the return count is only 24. We have narrowed this anomaly down to when
the speed signal is powered through the 9474 – that is, the data stream is
complete and correct, until this happens.
We suspected the control system was sending bad data, but we
placed a separate computer running a DOS character monitor on the RS 232 data
stream and is it complete and correct, Showing us that the full 78 bytes are
being transferred, but the Visa read is only producing the 24 bytes.
Then we tried another computer running a small VI that
simply reads the RS 232 data stream with Visa (its actually the same sub-Vi
doing the reading, but in a smaller easier to handle main VI). The data stream was interrupted on this
computer as well! Let me repeat this:
- Started
the engine simulation without the speed signal.
- Read
the RS-232 data stream with Visa (everything okay).
- Removed
the RS-232 cord from the main PXI system and attached it to the separate
computer (the data is still streaming, complete and correct coming from
the control system).
- Start
the speed signal external power to the 9474.
- The
data stream gets cut off at 24 bytes on the separate computer running the
Labview 8.0 VI with Visa 3.4.1
- Remove
the data cable and attach it to a third computer running a character based
data monitor and see that the data stream is complete (78 bytes) and
correct.
Since the DOS monitor reads the full stream, and both the
main computer running Visa 3.4.1 and the separate computer running Visa 3.4.1
only pass on 24 bytes, something seems to be going wrong in the Visa/serial
driver.
Any ideas?
Tony
I’ve attached the sub-Vi that reads the packet and the
FPGA.VI that drives the 9474 engine speed signal.
The rs-232 data stream is continuous and must be sync’d
using 4 sync bytes hex ‘FEFEFEFE’ – then the 78 packet bytes are read.
The engine speed section of the Fpga.vi is the second loop.
