Siemens SIMATIC S7-300 Reference Manual page 176

Digital Modules
Interrupts of the SM 322; DO 8 x 120/230 VAC/2 A ISOL
The SM 322; DO 8 x 120/230 VAC/2 A ISOL can trigger diagnostic interrupts.
The OBs and SFCs mentioned below are described in detail in the online Help for
STEP 7.
Enabling interrupts
The interrupts are not available – in other words, they are withheld without
appropriate parameter assignment. Use STEP 7 to assign parameters for enabling
interrupts.
Diagnostic interrupt
If you have enabled diagnostic interrupts, then active error events (initial
occurrence of the error) and departing error events (message after
troubleshooting) are reported by means of interrupts.
The CPU interrupts execution of the user program and processes the diagnostic
interrupt block (OB 82).
In the user program, you can call SFC 51 or SFC 59 in OB 82 to obtain more
detailed diagnostic information from the module.
The diagnostic information is consistent until such time as OB 82 is exited. When
OB 82 is exited, the diagnostic interrupt is acknowledged at the module.
Load restrictions with a horizontal configuration
With a horizontal configuration, the module loads must be restricted so that two
adjacent inputs or outputs do not exceed the maximum rating for an input or an
output.
Load restrictions with a vertical configuration
With a vertical configuration, the module loads must be restricted so that four
adjacent inputs or outputs do not exceed the maximum rating for an input or an
output.
3-92
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03