Peter M. Groen / libmodbus

Commit 1e62dd098d001d6966be28dfdf263995c7d136e5

Authored by Stéphane Raimbault
1 parent b4763407

Add information about not compliant devices (closes #219)

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Showing 1 changed file with 7 additions and 4 deletions
doc/modbus_set_slave.txt
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... ... @@ -22,12 +22,15 @@ The behavior depends of network and the role of the device:
22 22 *RTU*::
23 23 Define the slave ID of the remote device to talk in master mode or set the
24 24 internal slave ID in slave mode. According to the protocol, a Modbus device must
25   -only accept message holing its slave number or the special broadcast number.
  25 +only accept message holding its slave number or the special broadcast number.
26 26  
27 27 *TCP*::
28   -The slave number is only required in TCP if the message must reach a device
29   -on a serial network. The special value `MODBUS_TCP_SLAVE` (0xFF) can be used in TCP mode to restore
30   -the default value.
  28 +The slave number is only required in TCP if the message must reach a device on a
  29 +serial network. Some not compliant devices or software (such as modpoll) uses
  30 +the slave ID as unit identifier, that's incorrect (cf page 23 of Modbus
  31 +Messaging Implementation Guide v1.0b) but without the slave value, the faulty
  32 +remote device or software drops the requests! The special value
  33 +`MODBUS_TCP_SLAVE` (0xFF) can be used in TCP mode to restore the default value.
31 34  
32 35 The broadcast address is `MODBUS_BROADCAST_ADDRESS`. This special value must be
33 36 use when you want all Modbus devices of the network receive the request.
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