Siemens S5-100U - Mode of Operation for the External I;O Bus; The S5-100 U; Structure of the External I;O Bus

Technical Description S5-100U
2.2.2 Mode of Operation for the External I/O Bus
The S5-100U has a serial bus for the transfer of data between the CPU and the I/O 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.
A number of shift registers moves the data (Figure 2-5).
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 2-5. Structure of the External I/O Bus
Shift register of an
8-channel digital module
or of an analog module
n x 5 Bits
n=2, 4, 6 to 16
Shift register
of a slot
CPU
2
5 Bits
0 1 3
Slot number Data ring bus
2-6 EWA 4NEB 812 6120-02