Lenze Global Drive PLC Developer Studio - Manual (Page 10)

LenzeFpiDrv.lib function library
General information about the RS−232C interface
2−3
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LenzeFpiDrv.lib EN 1.1
2.3 Synchronous/asynchronous transmission mode
Serial data transmission distinguishes between synchronous and asynchronous transmission.
·
Synchronous transmission mode:
The data transmission between sender and receiver is synchronised by means of a clock
pulse. Thus the data cannot be send quicker than received and processed by the receiver.
·
Asynchronous transmission mode:
The data transmission is not synchronised by means of a clock pulse. The so−called
hand−shake method avoids data loss during the transmission.
The FP interface supports the asynchronous transmission mode only!
2.4 Data flow check (handshake)
With asynchronous data transmission the receiver must be able to inform the sender that it is not
ready for processing new or more data. The data flow check is called handshake. There are two
different handshake methods:
·
Hardware handshake:
The receiver controls the inputs CTS and/or DSR of the sender with its output DTR and/or RTS
via hardware cables.
– Advantage: transparent data transmission
– Disadvantage: additional cables required for the transmission of the handshake signals.
·
Software handshake:
The recipient sends special characters to the sender to control the data flow, e. g. XON/XOFF.
( ^ 2−5, ASCII character set)
– Advantage: Only data cables required for data transfer
– Disadvantage: The characters used for controlling the data flow must not be part of the user
data.
The FP interface supports the software handshake only!
2.5 Transmission parameters
With a serial, asynchronous data transmission the character to be transmitted is transmitted via the
data cable as bit sequence:
·
A bit sequence for a character is always started by a start bit which is send as logic "0".
·
The character is then transmitted as sequence of 7 or 8 bits starting with the least significant
bit (LSB).
·
The bit sequence for the character can be followed by a parity bit which can be used for
detecting transmission errors.
·
The bit sequence is ended by one or 2 stop bits, which are always send as logic "1".