Appendix I
151
Ap
p
en
d
ix
I
RS232 cable 15m at the longest
T +
T -
485-485+
485- 485+
485- 485+
1#
2#
N #
RS232 to RS485
converter
Frequency
inverter
Shielded twisted pair
PE
PE
PE
Frequency
inverter
Frequency
inverter
Figure I-4
The two longest distance inverter from the device shall short the terminal resistor on the control
board to be active. As shown in Figure I-5:
`
RS232 to RS485 converter
T +
T -
485-
485+
485-
485+
485-
485+
1#
2#
8#
RS232 cable 15m
at the longest
485-
485+
5#
Frequency
inverter
Frequency
inverter
Frequency
inverter
Frequency inverter
Figure I-5
Multi-machine connection should try to use a shielded cable. The basic parameters such as baud
rate and data bit of all of the devices on RS485 line must be the same, address must be different.
NOTE: The terminal resistor of 485 decides valid or invalid through the control board (No.
485) jumper
I-1-2 Protocol description
ST500 series inverter communication protocol is a asynchronous serial master-slave
communication protocol, in the network, only one equipment(master) can build a protocol (known as
“Inquiry/Command”). Other equipment(slave) only can response the "Inquiry/Command"of master by
providing data or perform the corresponding action according to the "Inquiry/Command"of master.
Here, the master refers to a Personnel Computer(PC), an industrial control device or a programmable
logic controller (PLC), etc. and the slave refers to ST500 inverter. Master can communicate with
individUal slave, also send broadcasting information to all the lower slaves. For the single
"Inquiry/Command"of master, slave will return a signal(that is a response) to master; for the
broadcasting information sent by master, slave does not need to feedback a response to master.
Communication data structure ST500 series inverter's Modbus protocol communication data
format is as follows: in RTU mode, messages are sent at a silent interval of at least 3.5 characters.
There are diverse character intervals under network baud rate,
which is easiest implemented. The first field transmitted is the device address.
