Only half-duplex mode can be used with an RS 485 (2-wire) setting.
Asynchronous Data Transmission
With the communication processor, serial transmission occurs asynchronously. The so-called
time base synchronism (a xed timing code used in the transmission of a xed character string)
is only upheld during transmission of a character. Each character to be sent is preceded by a
synchronization impulse, or start bit. The length of the start-bit transmission determines the
clock pulse. The end of the character transmission is signaled by the stop bit.
Declarations
As well as the start and stop bits, further declarations must be made between the sending and
receiving partners before serial transmission can take place. These include:
• Transmission speed (baud rate)
• Character and acknowledgment delay times
• Parity
• Number of data bits and
• Number of stop bits
Character Frame
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 set the desired format for data transmission with the
programming interface CP 440: Point-to-Point Communication, Parameter Assignment
interface.
By way of example, the gure below shows the two data formats of the 10-bit character frame.
Basic Principles of Serial Data Transmission
2.1 Serial Transmission of a Character
Point-to-point connection CP 440 Installation and Parameter Assignment
18 Equipment Manual, 03/2022, A5E00057742-AE
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