JXM-RS485-M1 expansion module
General description
The JXM-RS485-M1 expansion module is designed for connecting devices with an RS-485 interface to the controller. The module is intended for installation in JetHome series controllers JXD, which have mounting slots for JXM modules.
The module implements one galvanically isolated RS-485 channel.
The module’s operating logic depends on the user software (firmware) installed on the JXD controller.
Construction
The module is made as a single printed circuit board and is installed inside the JXD controller enclosure. The module has no enclosure of its own.
Revisions
Module revisions
v1.1
Initial version of the module
RS-485 interface
The module implements one RS-485 interface channel with galvanic isolation: the interface circuits are isolated from the other circuits of the module and the JXD controller.
The interface is implemented on the TDA51S485HC transceiver chip. Transmission direction switching is performed automatically; transmission direction control from the JXD controller is not required.
Maximum data rate over the RS-485 interface - 500 kbit/s.
The interface signals are brought out to the external four-terminal screw terminal of the JXM slot in which the module is installed:
Contact |
Purpose |
Description |
|---|---|---|
1 |
RS485-B |
Line B of the RS-485 interface |
2 |
RS485-A |
Line A of the RS-485 interface |
3 |
RS485-B |
Line B of the RS-485 interface |
4 |
RS485-A |
Line A of the RS-485 interface |
Contact numbering of the external screw terminal from left to right.
Contacts 3 and 4 duplicate contacts 1 and 2: this allows the module to be connected inline in the RS-485 bus without using additional terminal connections.
Line terminator
A built-in line terminator is installed on the module board - a 120 Ohm resistor. The resistor is connected to the RS-485 lines by setting the jumper TRM1 on the module board.
Note
The ends of the RS-485 bus must be terminated with 120 Ohm resistors on both ends. Jumper TRM1 is set only on the two end devices of the bus; on devices in the middle of the bus the jumper must be removed.
Connection to the JXD controller
The module is installed into any free JXM slot of the JXD controller motherboard and connects to the controller via the JXM IO connector: through this connector the module receives power and exchanges data with the microcontroller via the UART interface. The RS-485 interface signals are brought out to the external screw terminal through the JXM EXT connector.
The RESET and MODE signals of the JXM IO connector are not used by the module.
The number of JXM slots depends on the controller model, and the slots are connected to different UART ports of the microcontroller, so the configuration of the software depends on which slot the module is installed in. The number of slots, their designations and the purpose of the connector pins JXM IO and JXM EXT are given in the documentation for the controller, for example JXD-R6-E1ETH (v1).