GE GFK-1541B manual Monitoring the Channel Error Bit, Monitoring the Data Transfer Bit

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Monitoring the Channel Error Bit

This bit (normally 0) is the primary indicator for an error on a channel. It indicates any channel error, fatal or non-fatal. It does not necessarily indicate that the channel is down (idle). If this bit indicates an error:

ƒInitiate the Abort command and then reinitiate the Read or Write command, or if the error persists,

ƒInitiate the Retrieve Detailed Channel Status command to find out if the channel is down and possibly why it went down.

Keep in mind, however, that the status code may change from between the time the Channel Error bit indicates an error and the time the Retrieve Detailed Channel Status command retrieves the code.

The Channel Error bit for a channel is not meaningful until after the Ethernet Interface updates the CRS word confirming the Read or Write command for that channel. In the case of an Establish Channel command, the CRS word is updated before the Channel Error bit is set to 1.

Monitoring the Data Transfer Bit

Typically you will set up a channel to perform repetitive reads or writes. The Data Transfer bit pulses ( 0 → 1 → 0) each time there is a successful read or write. This can be an indicator to the ladder program to move the most recent data to another location.

The Data Transfer bit for a channel is not meaningful until after the Ethernet Interface updates the CRS word confirming the Read or Write command for that channel.

Do not use data received from a server until the CRS word confirming the Read command for that channel is 1 or the Data Transfer bit goes to 1. Do not assume that when the Data Transfer bit goes to 1 that a transfer has just completed during the last scan. The Data Transfer bit is not closely synchronized in time with the transfer. The bit only indicates that a transfer has occurred in a past scan. A rising edge on the Data Transfer bit indicating that a transfer has completed successfully does not guarantee that the next transfer has not begun or completed.

Sequencing Communications Requests

If the Ethernet Interface receives Command Blocks from the PLC CPU faster than the Interface can process them, the Interface will log an exception event 08, Entry 2=0024H and will log the PLC Fault Table entry:

“Backplane Communications with PLC Fault; Lost Request”

Only one COMMREQ function per channel can be pending at one time. A COMMREQ function is pending from the time it is initiated in the ladder program until its CRS word has been updated to a non-zero value by the Ethernet Interface.

GFK-1541B Chapter 3 Programming Channel Commands 3-47