McomRead

This function reads data from a device that uses the specified communication protocol. In most cases, this function actually reads the local computer's memory for data received from a controller (e.g. a PLC) during the controller's last write cycle. However, when communicating with the device using the Modbus protocol in master configuration, or reading configuration data from an EtherNet/IP device explicitly, this function can read the data directly from the device's memory. This function can also read the data last written to local memory using McomWrite().

A controller that uses the PROFINET protocol writes data to the local computer in modules in local memory. As such, you must specify the module's index from which to read the received data.

A controller that uses the Modbus protocol writes data to the local computer in data tables in local memory, when the local computer is in a slave configuration. To read from a Modbus device (either in a slave or master configuration), you must specify the data table from which to read.

A controller that uses the EtherNet/IP protocol writes data to the local computer, typically, in the consumer assembly in local memory. As such, to read data received from an EtherNet/IP controller, specify to read from the consumer assembly in local memory. You can also read from the producer or configuration assembly in local memory. When reading from a producer assembly, you are reading your own published data in local memory. When reading from a configuration assembly, you are reading EtherNet/IP configuration data in local memory about the local computer. Note that you can also specify another device on the network from which to read data explicitly, although this should only be used to read configuration data.

A controller that uses the CC-Link IE Field Basic protocol writes data to the local computer, in register and flag data tables in local memory. As such, to read data received from a CC-Link controller, you must specify whether to read the data in the flags or registers data table. The local computer can only be configured as a slave device.

For PROFINET and EtherNet/IP, use McomInquire() with M_COM_PROFINET_GET_MODULE_OUTSIZE or M_COM_ETHERNETIP_CONSUMER_SIZE to establish the size of the output module, or assembly, respectively, to which the controller has written. You must know how the module/assembly is divided into fields.

For CC-Link IE Field Basic, use McomInquire() with M_COM_CCLINK_TOTAL_OCCUPIED_STATION to learn the number of stations used by the industrial protocol instance. To establish the number of registers (RWw) or flags (RY) to which the controller can write, multiply the number of stations by 32 or 64 respectively.

If the time to execute this function is greater than the value set using McomControl() with M_COM_TIMEOUT, an error occurs.

This function is only available if you have the MIL Industrial Communication package, or another relevant update installed.