Lenze I/O system 1000 System Manual - Manual (Page 729)

Appendix
Serial process interfacing
Protocols
15
l
729 EDSIO1000 EN 7.0
15.1.1 Protocols
The following protocols are supported:
ƒ ASCII
ƒ STX/ETX
ƒ 3964(R)
)
Note!
Information on the parameterisation can be found in the corresponding
chapters regarding the fieldbuses.
ASCII protocol: Data communication via ASCII is a simple form of data exchange and can
be compared to a multicast/broadcast function.
The logical separation of the telegrams is effected via the character delay time. Within this
time, the transmitter must have sent its telegram to the receiver. A telegram is only
transferred to the higher−level system if it has been received completely. As long as the
"Time after request" has not elapsed, no new transmit request is accepted.
These two time specifications serve to establish a simple serial communication.
Since, apart from the use of the parity bit, no further backup measures are implemented
for ASCII transmissions, the data transfer may be very efficient, however, it is not secured.
With the parity the inversion of one bit within a character is secured. If several bits of a
character are inverted, this error can no longer be detected.
STX/ETX protocol: STX/ETX is a simple protocol with headers and trailers. It is used for
transmitting ASCII characters (20
h
7F
h
). This is done without block checks (BCC). If data
are to be read in by the peripherals, STX (Start of Text) must be available as initial character,
followed by the characters to be transmitted. An ETX (End of Text) must be inserted as the
terminating character. The user data, i.e. all characters between STX and ETX, are
transmitted to the control after the ETX terminating character has been received. When
data are sent from the control to a peripheral device, the user data are transmitted to the
EMP−S640 or EPM−S650 I/O compound module and are then transmitted to the
communication partner with STX as initial character and ETX as final character.
STX2 Z1 Z2 Zn ETX1 ETX2
ZVZ
STX1
SLIO_RS001
Fig. 15−1 Telegram structure
Up to two initial characters and final characters can be freely defined. Here, a "time delay
after command" can be selected for the transmitter as well.