Siemens SIMATIC CP 440 Manual page 22

Basic Principles of Serial Data Transmission
Character Frames
Data is transmitted between the CP 440 and a communication partner via the
serial interface in a character frame. Two data formats are available for each
character frame. 7 data bits without a parity bit are not supported. You can
parameterize the format for data transmission with the CP 440: Point-to-Point
Communication, Parameter Assignment parameterization interface.
By way of example, the figure below shows the two data formats of the 10-bit
character frame.
7 data bits, 1 start bit, 7 data bits, 1 parity bit, 1 stop bit
Signal state "1"
Signal state "0"
8 data bits: 1 start bit, 8 data bits, 1 stop bit
Signal state "1"
Signal state "0"
Figure 2-1
2-4
1 2
1 2
10-Bit Character Frame
Point-to-point connection CP 440 Installation and Parameter Assignment
8 9 10
9 10
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