ProSoft Technology MVI94-MCM-MHI - Manual (Page 61)

MVI94-MCM ♦ Flex I/O Platform Diagnostics and Troubleshooting
Serial Communications Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 61 of 109
March 29, 2011
4.4.2 Command Error List
Each command in the command list has a reserved word value for a status/error
code. This error data list can be read using the Configuration/Debug Port.
Additionally, the data can be placed in the virtual Modbus database of the
module. The configuration parameter "Command Error Pointer" defines the
register address in the virtual Modbus database where the data will be placed.
The first word in the register location defined contains the status/error code for
the first command in the port's command list. Each successive word in the
command error list is associated with the next command in the list. Therefore, the
size of the data area is dependent upon the number of commands defined.
Refer to the following Error Codes section to interpret the status/error codes
present in the data area.
4.4.3 Slave Status List
The slave status list views the communication status of each slave device on a
master port. Slaves attached to the master port can have one of the following
states.
0 The slave is inactive and not defined in the command list for the master port.
1 The slave is actively being polled or controlled by the master port and communication is
successful.
2 The master port has failed to communicate with the slave device. Communication with
the slave is suspended for a user defined period based on the scanning of the
command list.
Slaves are defined to the system when the module initializes the master
command list. Each slave defined will be set to a state of 1 in this initial step. If
the master port fails to communicate with a slave device (retry count expired on a
command), the master will set the state of the slave to a value of 2 in the status
table. This suspends communication with the slave device for a user specified
scan count (Error Delay Count value in the configuration). Each time a
command in the list is scanned that has the address of a suspended slave, the
delay counter value will be decremented. When the value reaches zero, the slave
state will be set to one. This will enable polling of the slave.
The slave status list can only be viewed using the module’s configuration/debug
port. The 'O' option on the main menu displays the status of all 256 slave units.
4.4.4 Error Codes
The module error codes are listed in this section. Error codes are separated into
Modbus error codes and module error codes.