Smb4: Queue Overflow; Special Memory Byte Smb4 (Sm4.0 To Sm4.7); Smb5: I/O Status; Special Memory Byte Smb5 (Sm5.0 To Sm5.7) - Siemens SIMATIC S7-200 System Manual

SMB4: Queue Overflow

As described in Table C-5, SMB4 contains the interrupt queue overflow bits, a
status indicator showing whether interrupts are enabled or disabled, and a
transmitter-idle memory bit. The queue overflow bits indicate either that interrupts
are happening at a rate greater than can be processed, or that interrupts were
disabled with the global interrupt disable instruction.
Table C-5
SM Bits
1
SM4.0
1
SM4.1
1
SM4.2
SM4.3
SM4.4
SM4.5
SM4.6
SM4.7
1
Use status bits 4.0, 4.1, and 4.2 only in an interrupt routine. These status bits are reset when
the queue is emptied, and control is returned to the main program.

SMB5: I/O Status

As described in Table C-6, SMB5 contains status bits about error conditions that
were detected in the I/O system. These bits provide an overview of the I/O errors
detected.
Table C-6
SM Bits
SM5.0
SM5.1
SM5.2
SM5.3
SM5.4 to
SM5.6
SM5.7
S7-200 Programmable Controller System Manual
A5E00066097-02

Special Memory Byte SMB4 (SM4.0 to SM4.7)

This bit is turned on when the communication interrupt queue has overflowed.
This bit is turned on when the input interrupt queue has overflowed.
This bit is turned on when the timed interrupt queue has overflowed.
This bit is turned on when a run-time programming problem is detected.
This bit reflects the global interrupt enable state. It is turned on when
interrupts are enabled.
This bit is turned on when the transmitter is idle (Port 0).
This bit is turned on when the transmitter is idle (Port 1).
This bit is turned on when something is forced.

Special Memory Byte SMB5 (SM5.0 to SM5.7)

This bit is turned on if any I/O errors are present.
This bit is turned on if too many digital I/O points have been connected to the
I/O bus.
This bit is turned on if too many analog I/O points have been connected to the
I/O bus.
This bit is turned on if too many intelligent I/O modules have been connected
to the I/O bus.
Reserved.
This bit is turned on if a DP standard bus fault is present
Special Memory (SM) Bits
Description (Read Only)
Description (Read Only)
C-3