How to use “Postive ack” and "Negtive ack" function in Serial gateway

1、Master station send a transaction to Slave station and need a response from slave in Request/Response protocols like Modbus RTU, If enable "Postive ack"、"Negtive ack" function in a transaction configuration, the positive ack data byte（1 byte） in the I/O data map is incremented each time when this transaction succeeds, the negative ack data byte(1 byte) in the I/O data map is incremented each time this transaction fails.

• Choose a transaction and enable "Postive ack"、"Negtive ack".
  
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• Enter "I/O data map" page ，the “√“  corresponse a "Postive ack" data byte ，the “ד corresponse a "Negtive ack" data byte， PLC can  judge data validity through the byte data value.
  

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2、For produce/consume communication protocols , produce transactions are send to serial device without response ，so produce transaction do not have "Postive ack"、"Negtive ack" function, but consume transactions can have "Postive ack" function.

• Beacuse of the length of "Postive/Negtive ack" data byte only is 1, so "Postive/Negtive ack" data byte max value is 255. If this byte exceeds 255,  the counting will restart from 0 to 255.
• For Modbus RTU protocol，If gateway access to wrong address of register of slave device or use a  function code that is not supported by slave device or other situation ,the slave device will response a exception code. The value of "Negtive ack" data byte value will be added 1 by gateway.
• Modify the length of gateway IO data in PLC configuration when enable ""Postive/Negtive ack" .