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Design, Functions and Operation
2.4.2
Mode of Operation of the External I/O Bus
The programmable controllers have a serial bus for the transfer of data between the CPU and the
S5-100U modules. This serial bus has the following characteristics.
•
The modular design permits optimal adaptation to the particular control task.
•
No addresses have to be set on the I/O modules.
•
A terminating resistor connector is not required.
•
Direct access to individual modules is not possible.
The data is moved via a number of shift registers (see Figure 2-6).
Four data bits and one check bit for bus monitoring are assigned to each slot in the bus unit. All
modules requiring more than four data bits have their own shift register and therefore do not have to
use the shift register of the particular slot.
Slot number
Basic unit
Shift register
of a slot
Shift register of an
8-channel digital module
or an analog module, ..., ...
2-8
Data ring bus
0
2
Figure 2-6. Structure of the External I/O Bus
4
5 bits
n x 5 bits
n = 2, 4, 8, 16
6
EWA 4NEB 812 6210-02
S5-95F
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