Levelcom 100 - The Hardware Menu

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Page 85

Verify that the Modbus Address is set correctly. See Modbus Communication in the

advanced Setup section of this manual.

Verify that the baud rate and parity settings are correct. There are some complications with

the parity settings, especially in the case where no parity information is sent. In

communications with desktop computers the most common parity setting is N-8-1, no parity,

8 bits per byte, 1 stop bit. In some PLCs though the only available no parity setting is

equivalent to N-8-2, no parity, 8 bits per byte, 2 stop bits. When there is a mix up between

these types the machines will communicate sometimes, but not reliably, or only in one

direction. The second stop bit can sometimes be detected as the start bit of the next byte if

an N-8-2 setup is communicating with a N-8-1 setup. This results in framing errors at the

receiving end and failed communication. See the Serial Communication section on page 30.

Under the COMM SETUP menu in the UTILITIES menu there is an item called DIAGS. The

standard Modbus error counters are accessible here and they can be useful to help

troubleshoot Modbus communication problems. The items in this menu are as follows

EVENT COUNT: Counts messages sent to the LevelCom 100 that were successfully

received and processed.

EXCEPTION COUNT: Counts messages sent to the LevelCom 100 that were successfully

received that generated exceptions. These are messages that cannot be serviced because

of parameters out of bounds, or there is a command that is not supported by the LevelCom

100.

MESSAGE COUNT: Counts all messages on the Modbus network, including messages not

directed at the LevelCom 100.

CRC ERROR COUNT: Counts messages sent to the LevelCom 100 who’s calculated CRC

did not agree with the CRC in the message. This suggests noise in the network is garbling

message traffic. If this counter is counting continuously check the network wiring for faults or

bad connections.

CLEAR COUNTERS: This utility is used to clear the Modbus counters. This is useful when

you start troubleshooting to see what the counters are doing now. If the network has been

operating continuously for a long time there may be non-zero count values on the error

counters even if the events counted are relatively rare. It is important to know if there is a

real problem or not. Clear the counters at the beginning of a troubleshooting session to

avoid confusion. The values of the error counters are also remotely readable through the

Modbus interface. See the Modbus register map section on page 91

The HARDWARE Menu

There is a special menu on the LevelCom 100 that is used to configure or read installed

hardware options. Most of these options are indications only and are not changeable by the