P201 Encoder Interface

The P201 series are single channel encoder interfaces suitable for use with a wide variety of 5V rotary and linear encoders. The USB versions allow encoders to be easily interfaced to and powered from a PC using only a USB cable. The new RS485 encoder interface (P201-9B-RS485) enables long distance, multidrop capability for SSI or BiSS C encoders.

Supported by PC based GUI Demonstration software and supplied with USB drivers that emulate a COM Port. Virtual COM Port access enables simple interfacing from LabVIEW, C#.Net, VB.Net, MATLAB.

More details can be referred to the data sheet of P201 interface.

% Function: encoderP201Read
% Author: Yu Xia
% Date: 2024.7.1 modified on 2024.10.8
% Institution: University of Melbourne
% Email: xiayudlut@icloud.com
% Description: This function communicates with an encoder via a serial port
% to read the encoder count, detect reference index, or clear/set the reference.
% It incorporates error handling to manage serial communication issues.
% The function returns three numbers: the encoder count, the count value at the 
% z-channel rising edge (reference index), and the status indicating if the reference 
% is detected.

function numbers = encoderP201Read(port, command)
    % Input:
    % port - Serial port identifier (e.g., 'COM5')
    % command - Command to send to the encoder ('?' for read, 'c' for clear reference, 'z' for set to zero)
    % Output:
    % numbers - A vector containing:
    %           [encoder count, count value at z-channel, reference status]
    %           or an empty array if the command is 'c' or 'z'

    % Set up parameters
    baudRate = 9600; % Baud rate for serial communication
    maxRetries = 3; % Maximum number of retries
    retryDelay = 0.5; % Delay between retries in seconds

    % Attempt to communicate with the encoder
    attempt = 0;
    success = false;

    while ~success && attempt < maxRetries
        attempt = attempt + 1;
        try
            % Initialize serial port
            sEncoder = serialport(port, baudRate);
            sEncoder.Timeout = 2; % Set timeout for serial communication
            
            % Flush the serial buffer
            writeline(sEncoder, 'v');
            pause(0.1);
            read(sEncoder, sEncoder.NumBytesAvailable, 'char');
            
            % Execute command based on the input
            switch command
                case '?' % Read encoder data
                    writeline(sEncoder, '?');
                    pause(0.1);
                    encoderStr = read(sEncoder, sEncoder.NumBytesAvailable, 'char');
                    pattern = '\d+'; % Regular expression to extract numbers
                    numbers = regexp(encoderStr, pattern, 'match');
                    numbers = str2double(numbers); % Convert string array to double array
                case 'c' % Clear reference status
                    writeline(sEncoder, 'c');
                    pause(0.1);
                    fprintf('\n Clear reference status \n');
                    numbers = [];
                case 'z' % Set current count value to zero
                    writeline(sEncoder, 'z');
                    pause(0.1);
                    fprintf('\n Set current count value to zero \n');
                    numbers = [];
                otherwise % Invalid command
                    error('Invalid command. Use ''?'', ''c'', or ''z''.');
            end
            % If everything went well, mark as success
            success = true;
        catch ME
            % Handle communication error and retry
            fprintf('Error: %s. Retrying...\n', ME.message);
            pause(retryDelay);
        end
        
        % Close serial port connection
        if exist('sEncoder', 'var')
            delete(sEncoder);
        end
    end
    
    % Check if communication was successful
    if ~success
        error('Failed to communicate with the encoder after %d attempts.', maxRetries);
    end
end

% Example Usage:
% 1. To calibrate the encoder and set the zero position:
%    encoderP201Read('COM5', 'z');
%
% 2. To read the encoder count, reference index, and status:
%    data = encoderP201Read('COM5', '?');
%    encoderCount = data(1); % Number of pulses read by the encoder
%    referenceIndex = data(2); % Count value at the reference index
%    referenceStatus = data(3); % Indicates if the reference is detected
%
% The difference between two encoderCount readings determines the 
% rotation angle, based on the encoder's resolution. For example, 
% with a resolution of 4000 PPR (pulses per revolution), 360 degrees 
% equals 4000 pulses. Therefore, 1.8 degrees corresponds to 20 pulses.
%
% After calibration, subtract the initial zero position count from 
% the current encoderCount to find the position relative to zero.

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