Example 13, Non-Blocking Delay; Example 14, Your Examples - CAI Networks WebControl PLC User Manual

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WebControl

PLC User Guide Version 3.02.17f

TAND 630 VAR3

The result for SIND and COSD is x1000, because we can only have integer on this

processor. The result for TAND is x100.

6.4.13 Example 13, Non-Blocking Delay

Non-blocking delay is expressed in PLC code as [] next to the operators. The

number inside [] is micro-seconds. The [] operation can be on both operators during

TST operations. Each input and output and VAR associated with a non-blocking

delay timer value. That value is set when I/O state is changed or VAR value being

modified. If later PLC instruction using non-blocking delay, that timer value will be

referenced. If current time is less than stored timer time plus the delay period, the

specified operation will not be performed. Reading value with non-blocking delay will

return false if timer value is not meet For example,

TSTGT VAR1[1500] IP1[300] RAM2

If any of those delay not reached, its result will be FALSE.

For SET VAR1[15000] IP1

VAR1 will not be set to IP1 value, unless 15000 milliseconds (15seconds) passed.

6.4.14 Example 14, WEBSET to get server reply

From 3.02.16 version firmware, WebControl allows PLC call WEBSET to do HTTP

GET call to HTTP servers inside another WebControl or other devices, or Apache or

IIS servers. The web server CGI code can process that information. From 3.02.17

version firmware, the web server can also send back to the WebControl a specially

formatted string. When WebControl received that string, it will set an internal variable

for user PLC code to reference. Following is an example CGI code from apache

server that will set the WebControl

in the WebControl. PLC program can

WSRPLY

base on that reply to turn on or off an I/O bit or take any other action.

Because PLC code does not execute WEBSET call immediately, rather WEBSET is

on a scheduler called from queue, user can not expect to get server reply

immediately after WEBSET call. The good practice would to check if the WSRPLY

value is zero, if that is zero, the server reply has not fetched back yet. Server must

return a non-zero value back. If WSRPLY is non-zero, user PLC must read it into

another variable and set it to zero, so that it can be used for next WEBSET call. In

this sense, if PLC logic wants to get multiple values from server reply, it must issue

one call at a time to avoid different WEBSET call return value clashing.

6.4.15 Example 15, Server CGI Handles WEBSET

The code below is for demonstration only, it is written in C on apache server. We do

not provide support for writing server CGI code. Please note to get the best result,

server CGI code should write back the string as early in the reply as possible. In

HTTP server reply processing, server mostly after sending reply will close

connection. If the "SET_WC=2147483647" string sending out too late, it could get

lost because the connection is closed already. Please test and make sure your

server is response fast enough for the WEBSET call.

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