Module Operation
3-2 SIMATIC 505-2571 Program Port Expander Manual
The
PPX:505-2571 is designed to work with operator interface devices which
adhere to the Non–Intelligent T
erminal Protocol (NITP). Up to four
supported devices may concurrently communicate with the controller
. The
PPX:505-2571 will provide buffering for the commands from the operator
interface and responses from the controller. Commands are sent to the
controller in the order they are received; no port has priority over any other
port. Only one command per port can be pending at a given time; a response
must be sent to the operator interface before a subsequent command will be
accepted. W
ith a few minor restrictions, the PPX:505-2571 port should
function the same as the controller program port.
NOTE: The ACTIVE indicator should remain on at all times after power up.
Should the ACTIVE indicator go out or exhibit a blink pattern, refer to the
troubleshooting section. When data is sent to a port the RCV indicator for
that port should light briefly
. Similarly
, when data is sent from a port the
XMT indicator should light briefly
.
This release of the PPX:505-2571 does not support T
ransparent Byte
Protocol (TBP). In addition, the PPX:505-2571 does not support an ASCII
print data stream.
Because the PPX:505-2571 is a Special Function module, the controller scan
time will be longer when the module is logged into the controller
. The effect
on scan time depends on several factors, including the type of request the
controller is processing and the number of requests processed per scan.
Some requests, such as a Read or W
rite memory location, can be processed
relative quickly
. Others, such as Find, consume significant controller CPU
resources.
The SIMA
TIC 545 CPU can process a maximum of eight requests per scan.
It is possible for the user
, via Aux 16, to set the number of requests (task
codes) that are processed each scan, for a minimum of one to a maximum of
eight. A lower number should normally result in a faster controller scan
time; the amount of increase depends on the type of request. However
, since
more requests can be processed each scan, this may improve data
throughput through the PPX:505-2571.
Ef
fect of Contr
oller
Scan T
ime