Siemens SIMATIC S7-300 Reference Manual page 117

Hardware interrupt lost
In an interrupt has been buffered for a channel and another interrupt occurs on that
channel before it has been processed by the CPU, a diagnostic interrupt "hardware
interrupt lost" is triggered.
More interrupts on this channel are not acquired until processing of the interrupt
buffered on this channel has been executed.
Interrupt-triggering channels
The channel triggered by the hardware interrupt is entered in the start information
of the OB 40 in the OB40_POINT_ADDR variable. Figure 3-9 shows the
assignment of the bits to the local data double word 8.
Byte
6/7
From
8
LB 8
31 30 29 28 27 26
1
Edge change: Channel 7
Figure 3-9 Start Information of OB 40: Which Event Has Triggered the Hardware Interrupt at the Limit
Value
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
Variable
OB40_MDL_ADDR
OB40_POINT_ADDR
LB 9
23 22 21 20 19 18
25 24
1 1 1 1
Edge change: Channel 15
Edge change: Channel 0
Edge change: Channel 1
Edge change channel 2
Data type
WORD B#16#0
DWORD See
Figure 3-9
LB 10
17 16
1 1 1
reserved
Edge change: Channel 8
Edge change: Channel 9
Edge change channel 10
Digital Modules
Description
Address of the interrupt
triggering module
Display of the interrupt
triggering inputs
LB 11
1 Bit no.
0
LD 8
3-33