Specifications

I
2
C Input/Output Boards, Continued
Switch SW1 located at the top of the board near the front (connector
end) controls the mode setting for the on-board digital inputs. The switch
sets the mode for all digital input circuits on the board (mixing of modes
on a board is not allowed). The available options are Default/Sink and
Legacy. The Legacy option is designed to adjust for a non-standard
configuration that may be in use on some systems. The Mode switch
should be set to Mode 2 unless instructed differently by Siemens.
DI Mode Switch
There are two standard I
2
C bus connections on the top of the board.
Either of these connections may be used as either a bus input or bus
extension connection. In this manner the I
2
C bus can daisy-chain from
one board to another or to other I
2
C devices.
I
2
C Bus Connections
The I
2
C I/O boards use an 8-bit board identification number as an
address on the I
2
C bus. The address is a hex number from 00 to FF,
corresponding to a decimal number from 0 to 255. Address numbers
from 1 to 254 are used (numbers 0 and 255 are reserved).
Address Switches
DIP switches are used to set the address for the physical board. When a
board is being replaced it is necessary to set the switches on the new
board to match the old board.
Figure 2-8: I
2
C I/O Address Switches
The DIP switches used to set the address are on the top back part of the
board and are labeled BOARD ID as shown in the figure above.
Together, the DIP switches correspond to an 8 bit binary number that is
set to match the board address. Each switch is labeled for the binary
digit it represents, and setting a switch is equivalent to setting that bit to
1. For example, in figure 2-8 above, the switches for 1, 2 and 4 are set
high. Thus, the board ID would be 1+2+4 = 7.
2-12 A5E31405710001