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Changes for page 05 Lua Script

Last modified by Devin Chen on 2025/03/04 14:07
From version 21.2
edited by Hunter
on 2022/12/13 12:04
Change comment: There is no comment for this version
To version 24.1
edited by Hunter
on 2023/03/01 12:01
Change comment: There is no comment for this version

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88 88  
89 89  = 10** How to parse value from subscribing MQTT topic** =
90 90  
91 -This example shows how to parse value from subscribing MQTT topic. The testing topic name is "testtopic/test/no1/123456".
91 +This example shows how to parse value from subscribing MQTT topic. Get the value and calculate the average value for group F1, F2, F3 and F4. The testing topic name is "testtopic/test/no1/123456".
92 +
93 +[[Download link>>https://ftp.we-con.com.cn/Download/WIKI/PI%20HMI/Demo/Lua%20Script/MQTT%20JSON%20parse.zip]]
94 +
92 92  And the subscribed content is like following:
93 93  
94 94  {{code language="json"}}
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209 209  }
210 210  {{/code}}
211 211  
212 - So we decode this json into lua object, and then assign the values from "Value" field into addresses HDW1~~HDW101, HDW112~~HDW202, HDW213~~HDW313, HDW324~~HDW424.
215 + So we decode this json into lua object, and then assign the values from "Value" field into table (addresses HDW1~~HDW101, HDW112~~HDW202, HDW213~~HDW313, HDW324~~HDW424).
213 213  
214 214  (% style="text-align:center" %)
215 215  [[image:MQTTScreen.png]]
216 216  
217 -
220 +Due to the MQTT code is not able to running on the simulator from PC, following picture is the testing result from actual HMI screen:
221 +
222 +(% style="text-align:center" %)
223 +[[image:MQTTactualtestingresult.png]]
224 +
225 +The JSON parser function is located on mqttAction.lua, called mqtt_msg_callback.
226 +
227 +(% style="text-align:center" %)
228 +[[image:MQTTJSONparsefunction.png]]
229 +
230 += **11 High-Low Byte Switch** =
231 +
232 +**{{code language="Lua"}}local lowByte = val & 0x00ff
233 +--take the lower 8 bits from address
234 +local shiftHigh = lowByte << 8
235 +--left shift 8 bits
236 +local highByte = val & 0xff00
237 +--take the higher 8 bits from address
238 +local shiftLow = highByte >> 8
239 +--right shift 8 bits
240 +local newVal = shiftHigh|shiftLow
241 +--bit or calculation{{/code}}**
MQTTJSONparsefunction.png
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1 +XWiki.Hunter
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MQTTactualtestingresult.png
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