R421A Relay Boards

These are inexpensive and readily available MODBUS multi-channel relay boards. Both 8 and 4-channel versions have been tested.

Device properties include:

Address

The address of a modbus slave. Modbus docs. call this the slave ID.

Node

Represents something a slave device does. Modbus relay boards have one node for each output it controls.

Node ID

The channel a node lives on. For the R421Axx relay boards this is the address or channel number. In a modbus transaction this is the address field.

8-channel

DIP switches set the slave address, from 0x00 to 0x3f. e.g. A0 ON=#1, A1 ON=#2, etc.

4-channel

Set A5 ON for MODBUS RTU mode (OFF is for AT mode).
Set A0-A4 to slave address, from 0x00 to 0x1f.

API

namespace R421A

Modbus/R421A/Device.h

Created on: 1 May 2018

This file is part of the IOControl Library

This library is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3 or later.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this library. If not, see https://www.gnu.org/licenses/.

R421A08 modbus 8-channel relay board

Channels are numbered 1 - 8. This is the 16-bit address field in a request.

To simplify operation we use a bitmask to specify relay states. We use the channel number directly so values can range between 0x0001 and 0x01FE

The query command returns a range of states, but other commands work with only a single channel. We therefore implement a mechanism to iterate through all requested channels using the same request.

There is a similar 4-channel board but with no markings and (as yet) no documentation. However all commands appear to work so a designation of R421A04 seems appropriate. Some typos in the 8-channel datasheet indicate that it was adapted from that of a 4-channel version.

R421A04 - 32 addresses set with DIP1-5, DIP6 ON for RTU mode R421A08 - 64 addresses set with DIP1-6, RTU mode only

Modbus/R421A/Request.h

Created on: 1 May 2018

This file is part of the IOControl Library

This library is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3 or later.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this library. If not, see https://www.gnu.org/licenses/.

Variables

constexpr uint8_t R421_CHANNEL_MIN = 1

constexpr uint8_t R421A_MAX_CHANNELS = 16

struct StateMask

#include <Device.h>

Tracks state of multiple relays.

Public Members

BitSet32 channelMask: Identifies valid channels.

class Device : public IO::Modbus::Device

#include <Device.h>

Public Functions

virtual IO::Request *createRequest() override

Create a request object for this device.

Return values:: Request* – Caller must destroy or submit the request

inline virtual DevNode::ID nodeIdMin() const override

Get minimum valid Node ID for this device.

Typically devices have a contiguous valid range of node IDs

inline virtual uint16_t maxNodes() const override

Determine maximum number of nodes supported by the device.

Return values:: uint16_t – 0 if device doesn’t support nodes

virtual DevNode::States getNodeStates(DevNode node) const override

Return the current set of states for all nodes controlled by this device.

Used to determine if, say, all nodes are ON, OFF or a combination.

virtual void handleEvent(IO::Request *request, Event event) override: Implementations may override this method to customise event handling.

struct Config

#include <Device.h>

R421A device configuration.

Public Members

Modbus::Device::Config modbus: Basic modbus configuration.

uint8_t channels: Number of channels (typically 4 or 8)

class Factory : public IO::RS485::Device::FactoryTemplate<Device>

#include <Device.h>

Public Functions

inline virtual const FlashString &deviceClass() const override: Return the Device class name, e.g. ‘r421a’.

class Request : public IO::Modbus::Request

#include <Request.h>

Public Functions

virtual ErrorCode parseJson(JsonObjectConst json) override: Fill this request from a JSON description.

virtual void getJson(JsonObject json) const override: Get result of a completed request in JSON format.

virtual bool setNode(DevNode node) override

If nodes are supported, implement this method.

/

/**

virtual DevNode::States getNodeStates(DevNode node) override: Query node status from response.

virtual ErrorCode callback(PDU &pdu) override

Process a received PDU.

Parameters:: pdu –
Return values:: ErrorCode – If request is re-submitted, return Error::pending, otherwise request will be completed with given error.