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This function is called from YOUR application code to perform a diagnostic check on a Modbus slave.

Prototype

CPU_INT16U  MBM_FC08_Diag (MODBUS_CH  *pch, 
                           CPU_INT08U  slave_node,
                           CPU_INT16U  fnct,
                           CPU_INT16U  sub_fnct,
                           CPU_INT16U  *pval);

Arguments

pch

is a pointer to the channel (returned by MB_CfgCh()). This pointer specifies onto which channel the Modbus master will be communicating on. Of course, ‘pch’ must have been configured as a Master when you configured the channel.

slave_node

specifies the slave ‘node address’ of the slave you want to perform a diagnostic function to. This can be a number between 1 and 255 but needs to match the number assigned to the slave node.

fnct

specifies the function you want to perform on the slave and you must specify either:

MODBUS_FC08_LOOPBACK_CLR_CTR

You want to clear the loopback counters in the slave.

MODBUS_FC08_BUS_MSG_CTR

You want to read the counter of messages received by the slave. This counter keeps track of all messages received whether processed or not.

MODBUS_FC08_BUS_CRC_CTR

You want to read the counter of bad CRCs detected by the slave.

MODBUS_FC08_BUS_EXCEPT_CTR

You want to read the counter of exceptions detected by the slave.

MODBUS_FC08_SLAVE_MSG_CTR

You want to read the number of message received and processed by the slave.

MODBUS_FC08_SLAVE_NO_RESP_CTR

You want to read the number of messages that have not been replied to because of bad CRCs, invalid commands, etc.

sub_fnct

corresponds to a sub-function argument for the function. At this time, µC/Modbus does not support sub-functions.

Returned Value

MODBUS_ERR_NONE

if the call was successful.

MODBUS_ERR_RX

if a response was not received from the slave within the timeout specified for this channel (see MB_CfgCh()).

MODBUS_ERR_SLAVE_ADDR

If the transmitted slave address doesn't correspond to the received slave address

MODBUS_ERR_DIAG

If you specified an invalid diagnostic function code (i.e. not one of the function described in the ‘fnct’ argument).

MODBUS_ERR_SUB_FNCT

If you specified an invalid sub-function.

Notes / Warnings

None

Called By

Your Modbus master application.

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