Siemens Simatic S7-300 CPU 31xC Series User Manual

Debugging functions, diagnostics and troubleshooting
10.2 Overview: Debugging functions
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
10-3
Danger
Forcing with S7-300 CPUs
The force values in the process image of the inputs can be overwritten by write commands
(such as T IB x, = I x.y, Copy with SFC, etc.) and by read I/O commands (such as L PIW x)
in the user program, or by write PG/OP functions! Outputs initialized with forced values only
return the forced value if not accessed by the user program via peripheral write instructions
(TPQB x, for example) or by PG/OP write functions!
Always ensure that forced values in the I/O process image cannot be overwritten by the
user program or PG/OP functions!
TPAW
OS
PAE
transfer
User program
Force value
OS: operating system processing
PAA
transfer
OS
PAE
transfer
Force value
For S7-300 CPUs, forcing corresponds to "cyclical controlling"
PAE
transfer
Executing
Force job
for inputs
Executing
Force job
for inputs
Executing
Force job
for outputs
Executing
Force job
for outputs
Force value
overwritten
by T PAW
Figure 10-1 Principle of forcing in S7-300 CPUs

Siemens Simatic S7-300 CPU 31xC Series Specifications

General

Series	S7-300 CPU 31xC
Power Supply	24 V DC
Communication Interfaces	MPI, PROFIBUS DP
Programming Languages	LAD, STL, FBD, SCL
Operating Temperature	0°C to +60°C
Memory	48 KB - 512 KB
Dimensions	40 x 125 x 130 mm (varies by model)