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Model S4000T

8.6 Exception Responses and Exception Codes

8.6.1 Exception Response

In a normal communications query and response, the master device sends a query to

the S4000T and the S4000T receives the query without a communications error and

handles the query normally within the master device’s allowable timeout. The S4000T

then returns a normal response to the master. An abnormal communications

produces one of four possible events:

1) If the S4000T does not receive the query due to a communications error, then no

response is returned from the S4000T and the master device will eventually process

a timeout condition for the query.

2) If the S4000T receives the query, but detects a communication error (CRC, etc.),

then no response is returned from the S4000T and the master device will eventually

process a timeout condition for the query.

3) If the S4000T receives the query without a communications error, but cannot

process the response to the master within the master’s timeout setting, then no

response is returned from the S4000T. The master device will eventually process a

timeout condition for the query. In order to prevent this condition from occurring,

the maximum response time for the S4000T is 200 milliseconds. Therefore, the

master’s timeout setting should be set to 200 milliseconds or greater.

4) If the S4000T receives the query without a communications error, but cannot

process it due to reading or writing to a non-existent S4000T command register, then

the S4000T will return an exception response message informing the master of the

error.

The exception response message (ref. No. 4 above) has two fields that differentiate it

from a normal response:

Byte

Modbus Range Referenced to S4000T

Slave Address 1-247* (Decimal) S4000T ID (Address)

Function Code 83 or 86 (Hex) MSB is set with Function Code

Exception Code 01 - 06 (Hex) Appropriate Exception Code (See Below)

CRC Lo 00-FF (Hex) CRC Lo Byte

CRC Hi 00-FF (Hex) CRC Hi Byte

8.6.2 Exception Code

Exception Code Field: In a normal response, the S4000T returns data and status in

the data field, which was requested in the query from the master. In an exception

response, the S4000T returns an exception code in the data field, which describes

the S4000T condition that caused the exception. Below is a list of exception codes

that are supported by the S4000T:

General Monitors S4000T User Manual

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