Table 1-7 Communication - Siemens CPU 31 Series Technical Data Manual

Communication
3.2 Communication services
Send and receive conditions
Conditions which should be satisfied for GD communication:
• For the transmitter of a GD packet:
• For the receiver of a GD packet:
A GD packet may be lost if you do not adhere to these conditions. The reasons being:
• the performance of the "smallest" CPU in the GD circuit
• asynchronous transmitting / receiving of global data at the stations
When setting in STEP 7: "Transmit after each CPU cycle", and the CPU has a short scan
cycle time (< 60 ms), the operating system might overwrite a GD packet of the CPU before it
is transmitted. The loss of global data is indicated in the status box of a GD circuit, if you set
this function in your STEP 7 configuration.
GD resources of the CPUs
Table 3-4
Parameters
Number of GD circuits per CPU
GD packets transmitted per GD circuit
GD packets transmitted by all GD circuits
GD packets received per GD circuit
GD packets received by all GD circuits
Data length per GD packet
Consistency
Min. reduction ratio (default)
3-10
Reduction ratio
transmitter
Reduction ratio x cycle time
receiver
< reduction ratio
transmitter
GD resources of the CPUs
x cycle time ≥ 60 ms
transmitter
receiver
x cycle time
transmitter
CPU 31xC, 312, 314 CPU 315-2 DP, 315-2 PN/DP,
Max. 4
Max. 1
Max. 4
Max. 1
Max. 4
Max. 22 bytes
Max. 22 bytes
1 (8)
317-2 DP, 317-2 PN/DP,
319-3 PN/DP
Max. 8
Max. 1
Max. 8
Max. 1
Max. 8
Max. 22 bytes
Max. 22 bytes
1 (8)
CPU 31xC and CPU 31x, Technical Data
Manual, 01/2006 Edition, A5E00105475-06