Basic Principles of Serial Data Transmission
2.3 Transmission integrity
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
36 Manual, 09/2008, A5E02191071-01
Transmission Integrity with the Printer Driver
Data integrity when using the printer driver:
● No data integrity precautions are taken for data transport with the printer driver.
● To prevent data from being lost in the event of the printer receive buffer overflowing, you
can work with data flow control (XON/XOFF, RTS/CTS).
● When data is output to the printer, the printer's BUSY signal is evaluated. The CP 341
receives the BUSY signal as a CTS signal and evaluates it in the same way (see ASCII
driver). Note that, when using CTS/RTS flow control, you must set the polarity of the
BUSY signal to CTS = "OFF" on the printer.
Transmission Integrity with the ASCII driver
Data integrity when using the ASCII driver:
● When data is transmitted via the ASCII driver, there are no data integrity precautions
other than the use of a parity bit (can also be canceled, depending on how the character
frame is set). This means that, although this type of data transport has a very efficient
throughput rate, security is not guaranteed.
● Using the parity bit makes it possible to detect an inverted bit in a character that is to be
transmitted. If two or more bits of a character are inverted, this error can no longer be
detected.
● To increase transmission integrity, a checksum and length specification for a message
frame can be employed. These measures must be implemented by the user.
● A further increase in data integrity can be achieved by means of acknowledgment
message frames in response to send or receive message frames. This is the case with
high-level protocols for data communication (ISO 7-layer reference model).
Transmission Integrity with 3964(R)
Enhanced data integrity through use of the 3964(R) procedure:
● The Hamming distance with the 3964(R) is 3. This measures the integrity of a data
transmission.
● The 3964(R) procedure ensures high transmission integrity on the transmission line. This
high transmission integrity is achieved by means of a specified message-frame setup and
release as well as the use of a block check character (BCC).
Two different procedures for data transmission can be used, either with or without a block
check character:
● Data transmission without a block check character: 3964
● Data transmission with a block check character: 3964R
In this manual, the designation 3964(R) is used when descriptions and notes refer to both
data transmission procedures.
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