Hi,
I came across a situation for which I don't get a clear definition from the Modbus Application Protocol Specification (v1.1b3). It's about the MEI type 14 "read device identification" as part of Function Code 43 "encapsulated interface transport".
Let's assume that a device supports basic and regular category:
With stream access, the device returns all objects from the requested category starting at the object id stated in the request.
But how should the device respond if the object id is not within the category, i.e., a mismatch between ReadDevId code and object id?
Examples:
1. Request for basic category with stream access and object id 5 (which is in regular category):
req.PDU: 2B 0E 01 05
2. Request for regular category with stream access and object id 1 (which is in basic category):
req.PDU: 2B 0E 02 01
I get two possible behaviors from the specification:
Figure 30: Object Id OK = NO -> Exception Code 02 "illegal data address"
I'm curious to know your opinion
I came across a situation for which I don't get a clear definition from the Modbus Application Protocol Specification (v1.1b3). It's about the MEI type 14 "read device identification" as part of Function Code 43 "encapsulated interface transport".
Let's assume that a device supports basic and regular category:
With stream access, the device returns all objects from the requested category starting at the object id stated in the request.
But how should the device respond if the object id is not within the category, i.e., a mismatch between ReadDevId code and object id?
Examples:
1. Request for basic category with stream access and object id 5 (which is in regular category):
req.PDU: 2B 0E 01 05
2. Request for regular category with stream access and object id 1 (which is in basic category):
req.PDU: 2B 0E 02 01
I get two possible behaviors from the specification:
vs.If the Object Id does not match any known object, the server responds as if object 0 were pointed out (restart at the beginning).
Figure 30: Object Id OK = NO -> Exception Code 02 "illegal data address"
I'm curious to know your opinion