Design, Functions and Operation S5-95F
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.
Figure 2-6. Structure of the External I/O Bus
Shift register of an
8-channel digital module
or an analog module, ..., ...
n x 5 bits
n = 2, 4, 8, 16
Shift register
of a slot
4
5 bits
2 6
Slot number
Data ring bus
Basic unit
0
2-8
EWA 4NEB 812 6210-02
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