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Serial Communication

The serial module is used to communicate from RoboRealm to serial based controllers. The module can be used to communicate to SSC, Parallax, etc. type controllers. Before embarking on using the serial module check that the specific device is not already supported by another RoboRealm module as that will be easier than understanding and implementing a particular device's protocol.

The serial module allows you to configure the serial port for various communication parameters (baud rate, stop bits, etc.) and specify the communication protocol for initializing, sending and receiving data. The text boxes allow you to enter in the necessary command numbers for each respective sequence type (read or write).

Interface

Instructions

1. Port - Select the COM port to use. Note that COM1-4 are typically assigned directly to hardware ports. COM5+ are typically assigned to virtual ports created by USB devices.

2. Baud - Specifies how fast communication will occur between the PC and serial device. Typically rates are 9600 with the fastest being 115200. Note that if you see irregular characters being received from the serial device this many indicate a mismatch between baud rates.

3. Data Bits - Indicates how many bits are reserved for data communication between the serial device and the PC. Typical value is 8.

4. Parity - Indicates what kind of error checking that is performed during serial communication. Even means the last bit is set to ensure that an even number of bits are used, whilst odd means the last bit is set to ensure that an odd number of bits are used. When the receiving side sees a discrepancy (i.e. an odd number of bits being transmitted when even parity is required) the device knows a transmission error has occurred. Typical value is None.

5. Stop Bits - Refers to how many bits are used to indicate a delimiter between data bits.

6. Flow Control - Allows you to set the flow control options for the serial device. By default RoboRealm sets all flow control to off/disabled. By clicking on the Flow Control button you can set the following options

XON/XOFF for both transmission and reception
CTS/DRS (clear to send)/(data set ready)
DTR/RTS (data terminal ready)/(request to send)

7. Wait for reply - Forces the module to wait for a reply after characters have been sent. This ensures that the module pauses until a reply has been received from the remote device. Note, this can cause the pipeline to slow down due to the pause for a reply. Only select this checkbox if you require a reply before continuing the pipeline.

8. Session Timeout - when receiving information from a serial device this number represents how long the module will wait for a character until giving up and resetting the connection. Note that the value is in milliseconds, where 1 second = 1000 milliseconds. The default is 5000 or 5 seconds.

9. Message Timeout - When receiving information from a serial device this number represents how long the module will wait for the next character until giving up and assuming the message is complete. Note that the value is in milliseconds, where 1 second = 1000 milliseconds. The default is 100 or 0.1 seconds. This is very useful when no delimiter is specified and a complete message is determined by the lack of new characters for a small period.

10. Console - if the device supports reading you will start to see a large amount of numbers scrolling by in the console. This shows the current values being read from the device and provides a log of the ongoing communication activities. The green text is from RoboRealm, the red text are characters received and the green text are characters sent by RoboRealm to the device. To copy the log click on the Copy button, likewise to clear it click on the Clear button. Note that the console log only shows several lines at a time with older information being discarded.
You can switch the output to various formats for better viewing:

ASCII - shows the data as ASCII characters. Any character outside of printable characters will be represented with a \ followed by the actual integer data that was read

Decimal - shows the data as sets of single byte integer numbers

Hexadecimal - shows the data as sets of hexadecimal numbers (base 16 numbers, e.g. FF)

Short Binary - shows the data as binary numbers with prefix 0's removed

Binary - shows the data as sets of single byte binary numbers

11. Send Now - often you need to quickly test the device by sending a certain sequence of characters. To do so just type in the character sequence (using for carriage return, [image_count] for variables, etc.) and click on Send Now. The text will be parsed and sent to the serial device and the response will then appear in the console log. Note that this is different from the send sequence which will be sent each time the serial module is encountered in the processing pipeline. The Send Now button is a manual testing mechanism meant for debugging purposes. Also note that the returned text will be parsed by the Receive Sequence so that you can test your parsing code and see if the variables have been created. Use the Watch Variables module to see those variables being created.

12. Refresh Rate - to slow the scrolling of the numbers select a different refresh rate for the console. This will just slow down how quickly RoboRealm reads information from the device.

13. Initialization Sequence - The initialization data sequence sends the provided string to the serial device on initialization of communication. You may want to use this to command the receiving device into a specific mode ready for communication with RoboRealm. This initialization sequence is sent each time the serial communication is reset. This happens when you click on the "Stop" button in this interface, change one of the above parameters (Baud, Port, etc) or when the RoboRealm starts running for the first time. It is NOT sent when the Run button in the main RoboRealm interface is toggled. See the Text Formats page for additional information about the text string format.

14. Send sequence - Used to enter commands sent per pipeline loop (i.e. image processed) by RoboRealm. You can use this sequence to transmit variables created by other RoboRealm modules to the serial device. Each time an image is captured and processed the serial module will interpret the Send Sequence text and send the result to the serial device. See the Text Formats page for additional information about the text string format.

15. Enable - Allows you to temporarily disable sending text to the serial device while performing edits. Note that the Send Sequence textarea will turn red to indicate this setting.

16. Send Rate - Some serial devices cannot handle data streams even given a slower baud rate. Use this dropdown to select how quickly you want the data to be sent. At AFAP (As Fast As Possible) the data will be sent out about 30 times a second (this assumes a camera running at 30 fps).

17. Clear serial buffer trigger - there are cases when too much data may be buffered on the serial port that needs to be cleared due to some event. In this case specify a variable whose value when set to "clear" will remove all data scheduled to be sent over the serial port.

18. Send only on change - If your data does need to be sent out to your serial device every iteration through the processing pipeline loop this selection will prevent the same data from being sent to the serial device that was last sent. This is also an elegant way to reduce the data bandwidth to the device if your sequence does not change rapidly.

19. Receive sequence - used to receive and parse text send from the serial device. The text string is matched against the incoming serial bytes. When a match is found variables are added into RoboRealm for use in other modules. Reading into variables just requires adding in a variable at the appropriate spot within the receive string similar to the scanf routine in C/C++. The Receive sequence works similar to an expect string, i.e. you need to specify patterns that match the incoming text and substitute the areas that need to be fed into variables with the [ variable_nane ] format. Note that even if you are missing one space or newline the patter will not match and the variable will be zero or blank. See the Text Formats page for additional information about the text string format.

20. Test Receive - instead of waiting for the correct data bytes to come from your serial device you can type in a test sequence that will be parsed by the receive sequence. This can be handy when first testing that your receive sequence is picking up the right bytes.

To learn more about what text can be used in the the Sequence boxes please refer to the Text Formats page.

Example

To read digital inputs from a VEX Robotics System robot over the serial port you can configure the settings to port COM5, baud 115200, 8 data bits, no parity, 1 stop bit with the sequences as:

Initialization Sequence
\x0f\x0f\x08\x40\xb8\x04

Send Sequence
\xaa\x55\x00\x00\x00\x0B\x00\x00

Receive Sequence
DIN [din1] [din2] [din3] [din4] [din5] [din6]<lf>

which would command the Vex in the online mode (be sure to download that code to your Vex robot) and read in the digital inputs into variables din1, din2, din3, etc. You can add the Watch Variables module to see these variables change when you press a bump switch on the Vex.

Note that the Vex online mode needs to be downloaded prior to using this serial sequence. Be sure your Vex is reacting to the online interface provided by Vex to ensure correct online operation.

See Also


MCU Communicator
SSC
Parallax

For more information


CodeGuru: Serial Communications in Windows
The Code Project: Serial library for C++

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