Astralpool Control Basic Plus Installation Manual page 6

3.1.2 BUS ISOLATION AND TERMINATION RESISTORS
If the communication bus is accessible by the user, it shall be double insulated. In general, the accessibility of the bus to
users will depend on each installation; safety isolation has been implemented in the pump's physical bus layer.
Moreover, for safety purposes, it is recommended to ensure that other devices sharing this bus also implements this
insulation. Additionally, the use of bus insulated devices also increases the equipment reliability, larger immunity to
electromagnetic interference, longer life, and more stability over the range of temperatures. Whenever single or multiple
devices are sharing a bus physical connection, it is recommended to use terminating resistors at the ends of the bus,
even more so when use large cable length or high speed data rates. The terminating resistor is used to prevent an RF
signal from being reflected back from the end, causing interference. The terminating resistor must be in both ends of the
bus, connected in parallel (as shown in the image below). A typical value of this resistance is 120Ω, 0.5W. The value of
the resistor must be the same in both ends. The terminating resistors are labelled "R_T" in the diagram.
4 MODBUS FUNCTIONS
4.1 FUNCTIONS SUPPORTED
Please, be careful when issuing MODBUS commands, and make sure that the function used is correct.
REGISTER ACCESS MODE
Functions in register access mode are implemented according to the MODBUS-RTU standard described in
http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf In general registers are unsigned 16 bit coded.
0x03 READ HOLDING REGISTERS
0x04 READ INPUT REGISTERS
0x10 WRITE MULTIPLE REGISTERS
4.2 EXCEPTION RESPONSES
Exception responses are implemented according to the MODBUS-RTU standard, described in the chapter MODBUS
exception responses: http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf
The exceptions implemented are: 1,2,3 and 6.
5 DEVICE DESCRIPTION AND CONFIGURATION
5.1 GENERAL DESCRIPTION
Using MODBUS commands, the pump's set-point can be changed, also, various state and diagnostic information can be
retrieved.
When a simultaneous request is made through MODBUS, the front panel has the priority. It's possible only to read
certain parameters.
It is the operator's responsibility to check that values sent are consistent with the application.
In this manual, the numbers in hexadecimal have been represented with the format 0xZZ, where ZZ is the number.
0000138174
Image 4. Interconnection of devices
rev.1.1 4