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Integration

This section provide a top level aspect on how to integrate the W-Modbus module into a product.

Overview

Presented below is an over head block diagram of components required for integration of the module. The module itself needs to be soldered on to a carrier board.

Module Overview Block diagram of a W-Modbus module

In order to fully integrate the module into a product the carrier board needs to provide the following interfaces:

  • RS485 - for external connection between other Modbus devices and the module. For an example see Reference design for RS485 circuit.
  • SPI or UART management interfaces - for communication with the W-Modbus device, and to configure its RS485 communication parameters. The product designer can choose any of the options, they have the same capabilities.
  • Push button - press while powering up the device to put it into DFU/bootloader-mode. It is also possible to pull the bootloader/button pin high to 3.3 V while powering on the device. However, it is also possible to enter this mode using the SPI or UART management interfaces (without having to manually power on or off the device).

A complete integration also requires:

Power supply recommendations

The W-Modbus Module is designed for 3.3 V operation. Do not apply power to any of the pins until the 3.3 V rail is connected.

To ensure reliable operation, the supply pin should be decoupled with a 100 nF ceramic capacitor close to the supply pin. It is also recommended to add a high value ceramic bulk capacitor, such as 47 uF, which will reduce the current ripple of the 3.3 V net.

During radio transmission, current consumption will rise sharply to 150 mA typical, 250 mA max. A typical slew rate value is 300 A/s during radio transmission.

Symbol Parameter Min. Typ. Max. Unit
VDD Supply voltage 3.0 3.3 3.6 V
Vrise Supply rise time (0 V to 3.7 V) 60 ms
IDD Supply peak current capability 150 250 mA
IDD_rate Supply current slew rate 300 A/s

Common mistakes

The integration of the W-Modbus module is a relatively simple process, but for optimal RF performance it is important to follow the power supply and layout considerations. Failure to do so may result in inferior RF performance. Some important highlights to avoid the most common mistakes are shown below:

  • The carrier PCB shall be of the recommended type and have a proper ground plane
  • Product enclosure and carrier PCB shall adhere to the clearance recommendations
  • Product enclosure shall not block radio-signals
  • Power supply pins shall have sufficient decoupling
  • All ground pins shall be available on the carrier PCB
  • Programming pins (P20 and P21) shall be accessed
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