Siemens 505-2571 - Manual (Page 25)

Troubleshooting 4-3 SIMATIC 505-2571 Program Port Expander Manual
If the XMT indicator does not flash within 2 seconds of receiving a signal
(RCV indicator flashes), it indicates that the PPX:505-2571 is not
responding to the signal. Refer to the information below for possible causes.
First, check to ensure that the baud rate settings on both the PPX:505-2571
and the operator interface are set to the same data rate. If you note a
problem, set both to the same baud rates and retry.
NOTE: You must remove power from the PPX:505-2571 module, change the
DIP switch settings, and repower the module before the new baud rate
selection will become effective.
If you are using a RS–232 port and your device is NOT configured for
hardware handshaking, ensure that hardware handshaking is DISABLED
(DIP switch position 3 for the port in the OFF position). See Table 2-1 and
Figure 2-1.
If you are using a RS–232 port and your device is configured for hardware
handshaking, ensure that the handshaking wires are properly connected
(see the documentation for the connected device). In some cases you can
check out a handshake wiring problem by temporarily setting hardware
handshaking to DISABLED (port DIP switch position 3 set to the OFF
position). If the PPX:505-2571 responds to the attached device (XMT LED
flashes), then you probably have a wiring problem.
The attached device must issue and respond to task code packets as defined
in the Non–Intelligent Terminal Protocol (NITP). If you are unsure of this
fact, you can attach the device directly to the programming port to
determine if it works properly. If it does not work and cabling/configuration
items discussed in other sections above have been checked, then you
probably have a protocol problem. If it does work, there is still a chance that
the device is using Transparent Byte Protocol (TBP), which is not supported
in this version of the PPX:505-2571. Most application programs and
operator interface devices that can use TBP allow you to force the use of
Non–Intelligent Protocol (NITP), which is supported.
If you experience intermittent communications failures, you may be
experiencing noise on the communications cable which interferes with data
transmission. If you are communicating at rates higher than 1200 baud, you
can reduce the baud rate to check for improvement. If reducing the baud
rate does correct the proble, you most likely have a noise problem. You
should first ensure that you have not exceeded the maximum distances for
cabling lengths (50 feet for RS–232 and 4000 feet for RS–422). Also check
for proper grounding of the cable shields; we recommend connecting the
shield at one end only. Longer cable runs may be subject to ground loops;
you may require the addition of an electrical isolation device.
Module Response
Problems
Baud Rate
Mismatch
Hardware
Handshaking Error
Protocol Problems