Crimson Raw Serial RS-485 Request/Response Example

Overview

This technical note demonstrates a request/response exchange using a Crimson Raw Serial Port. The transmit program clears the receive buffer and sends a command. The receive program waits for a carriage-return-terminated response, writes non-empty data to a tag, and calls the transmit program again.

Applicable Products and Versions

• Crimson 3.2-based products
• The exact hardware model and firmware version were not provided.

Prerequisites

• Configure and enable a Raw Serial Port.
• Configure the serial port to match the connected device.
• Connect a device that accepts the transmitted command and returns a response terminated by a carriage return.
• Create a String tag named Basic.Response.
• Create a transmit program named Basic.Tx().
• Create a receive program named AdvancedNotAbbr.Rx().

Serial Port Configuration

The supplied configuration image shows these settings:

Transmit Program

// declare local variable
int port = 2;

// clear the port's buffer
ClearRx(port);

// print N01TA$ out of Port 2
PortPrint(port, "N01TA$");

Receive Program

// declare local variables
cstring input;
int port = 2;

// read Port 2's buffer: no start character, <CR> end character,
// 500 ms timeout, no length restriction
input = PortInput(port, 0, 13, 500, 0);

// check for non-empty input
if(input != "") {
    // populate tag with data
    Basic.Response = input;
}

// request more data
Basic.Tx();

Code Operation

Transmit Program

1. Assigns Port 2 to the local port variable.
2. Clears pending receive data from Port 2 with ClearRx().
3. Sends the ASCII string N01TA$ from Port 2 with PortPrint().

Receive Program

1. Declares the input string and assigns Port 2 to the local port variable.
2. Calls PortInput(port, 0, 13, 500, 0) to read the receive buffer.
3. Uses no start character and ASCII 13 (<CR>) as the end character.
4. Uses a 500 ms timeout and no length restriction.
5. Writes a non-empty response to Basic.Response.
6. Calls Basic.Tx() to request more data.

Applying the Code in Crimson

1. Configure the RS-485 communications port with the settings shown above.
2. Add the transmit code to Basic.Tx().
3. Add the receive code to AdvancedNotAbbr.Rx().
4. Create the String tag Basic.Response.
5. Set the Raw Serial Port On Update property to AdvancedNotAbbr.Rx().
6. Initiate the first transmission by calling Basic.Tx() from an appropriate Crimson event or action. The initiating event was not provided.
7. Download the database and monitor Basic.Response.

Validation

1. Confirm that Port 2 transmits N01TA$.
2. Confirm that the connected device returns a carriage-return-terminated response within 500 ms.
3. Confirm that the returned value is written to Basic.Response.
4. Confirm that Basic.Tx() is called after the receive attempt.

Troubleshooting

Limitations and Assumptions

• The example uses Port 2.
• The command is N01TA$.
• The expected response terminator is ASCII 13 (<CR>).
• The receive timeout is 500 ms.
• The example does not define the event that initiates the first call to Basic.Tx().
• The exact connected device, protocol, hardware model, and firmware version were not provided.