Structure And Operation Of The Control Word; Structure Of The Control Word - Siemens SIMATIC S5 Manual

General Operation
4.3.1

Structure and Operation of the Control Word

Control commands are transferred to the IP 265 via the control word. The IP 265 can thus be
switched to the STOP and RUN operating states.
Two types of instruction can be stored in the control word:
• Instructions reserved for COM 265
• Instructions accessible to the user (CPU user program).
Note
When the IP 265 is being checked by COM 265 (COM 265 instruction active), the CPU user
program may not write the output data for the IP 265 in the PIQ. This must be taken into
consideration for program generation (scan of the control bit in the status word of the IP 265;
Section 4.3.2).
General structure of the control word:
Byte 0
Byte 1
7 6
Instruction bits for users
Bits for COM 265-internal use
Note
Only the 2 instruction bits in byte 0 of the control word are relevant for the control of the
IP 265 by the CPU user program. Only one of the two bits may be set, where bit 0 is the
STOP bit and bit 1 is the RUN bit. The remaining bits of the control word are handled
independently by COM 265 and must not be overwritten by the user.
4-8
5 4 3 2 1
Figure 4-6. Structure of the Control Word
Instruction
Bit 1 Bit 0
code:
0
1
0
1
* Illegal instruction code sequence
** No transfer of parameters
0
IP 265
Response of IP 265
1
STOP
0
RUN
no change**
0
of the operating state
Instruction error indi-
1
cation* and STOP
EWA 4NEB 812 6130-02a