User Manual ECOSTEP®54
44
Subject to change without notice!
9.2
Data Protocol of the RS232 Interface
Generally, the behaviour of the RS232 interface is according to the CAN standard. Th e CAN pro-
tocol is „tunneled“, i.e., the data is transported within the CAN protocol via the serial interface.
As device address the CAN Node ID is used.
RS232 communication uses a strictly master slave relation. Th e host computer only can initiate
any data transfer sending a data telegram to the ECOVARIO® device listening on the TxD line of
the host. Th is device immediatly echoes this byte, i.e. every received byte is transmited to the next
device in the loop ensuring that each slave in loop will receive the host telegram. At the end of
the loop the host will receive the data was sent. Th e adressed ECOVARIO® device computes the
received data and sends an answer telegram. Depending on device position in the communicati-
on loop, this telegram is transported via echo from one device to next and fi nally to the host.
RS232 communication requires the following interface settings:
asynchronous communication
9600 baud, 8 data bits
no parity
1 stop bit
Th e transport protocol uses a telegram with a fi xed length of 10 bytes.
Th e host sends:
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5 Byte 6
Byte 7 Byte 8 Byte 9
ID
8 byte host data
CHKS
Der Host receives the echo (RS232):
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5 Byte 6
Byte 7 Byte 8 Byte 9
ID
8 byte host data
CHKS
Der Host receives the answer:
Byte 0
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5 Byte 6
Byte 7 Byte 8 Byte 9
ID
8 byte slave data
CHKS
ID is the ID No of the addressed slave
CHKS is the telegram checksum. CHKS = -∑(byte 0 .. byte 8)
Note:
Each 10 byte telegram has its own checksum.
If the host sends a telegram with an unused ID data will pass the loop but no slave answer will re-
turn. In that case the host will receive 10 bytes only. Th e slave fi nding its own ID in host telegram
checks the CHKS value. If the checksum does not match the slave would not generate an answer.
Acces to the object dictionary via RS232 will work in the same way as CANopen SDO, excluding
segmented data transfer. Th e 8 byte data of the SDO protocol are extended by 1 byte address
(node ID) and 1 byte checksum. Th e arrangement of the 8 byte data is described in the following.
Application of the PDO, SYNC, EMCY and NMT objects is not possible via RS232.
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