Introduction

The 171 CBU 78090, 171 CBU 98090 and 171 CBU 98091 processors can detect errors during run-time. There are 4 types of reported detected errors:

  • Local I/O detected errors

  • I/O-Bus detected errors

  • Minor CPU detected errors

  • Major CPU detected errors

Local I/O Detected Errors

A local I/O error is detected when:

  • The processor cannot read the ID of the I/O base.

  • The ID of the local I/O base does not match the configured I/O base.

  • The I/O base triggers the detection of an error

If a local I/O error is detected, the RUN LED blinks ON and OFF, and the ERR LED is ON.

When a local I/O error is detected, the current I/O transmission is dropped.

The cause of a detected local I/O-Bus error is stored in the register located at %SW135 with the following values:

  • 0 = no detected error

  • 1 = error detected while attempting to read the I/O base ID

  • 2 = I/O base mismatch detected (the I/O base ID does not match the I/O base ID in the application)

  • 3 = I/O base errors detected

I/O-Bus Detected Errors

An I/O-Bus error is detected when one of the following events occurs:

  • The ID of the remote processor does not match the configured processor ID.

  • The I/O base triggers the detection of an error.

  • The processor detects a missing or extra processor on the I/O-Bus.

  • The processor detects an I/O-Bus exchange error.

The cause of a detected I/O-Bus error is stored in the register located at %SW134 with the following values:

  • 0 = no detected error

  • 1 = module ID mismatch

  • 2 = I/O base errors detected

  • 3 = missing or extra module

  • 4 = detected bus exchange error

The processor also provides a compatibility status in a register located at %SW132, which is significant only when %S118 is set to 1. The compatibility status register can have the following values:

  • bits 0 to 14: Contain a value from 1 to 64, which indicates the network position of the module that cannot be reached.

  • bit 15:

    • A value of 0 indicates a general communication interruption.

    • A value of 1 indicates that communication with a module is possible, but the detected module is not of the configured module type.

Minor CPU Detected Errors

A minor CPU error is detected when the processor enters the Halt state. No action is needed to clear a minor detected error. The processor can continue to operate.

When a minor CPU error is detected, both the RUN and ERR LEDs blink ON and OFF.

Major CPU Detected Errors

When a major CPU error is detected, the processor enters the Stop state. The processor cannot continue to operate. A major CPU detected error can have many causes.

For diagnosing detected errors, use the following system words:

  • %SW125: last detected error

  • %SW126 and 127: address of the program instruction that generated the detected error

For a description of system bits and words, including detected error descriptions, refer to the System Bits and System Words topic in Control Expert help.

When a major CPU error is detected the RUN LED is OFF, and both the ERR and IO LEDs remain ON.

To clear a major detected CPU error, you need to cycle power to the processor. The processor performs a cold start, and restarts in Stop state.