Matlab List Serial Ports
Overview
- Matlab List Serial Portsmouth
- Matlab List Available Serial Ports
- Matlab Serial Port Example
- Matlab Serial Port Read
Matlab has a 'serial' function that allows it to communicate through a serial port. This project is to establish serial port connection with the PIC microcontroller and demonstrate bidirectional communication between the PIC and a Matlab program. For demonstration purposes, the PIC will send digital potentiometer readings to Matlab as well as receive keystrokes from the Matlab user to light up LEDs on its circuit board.
A USB to RS232 adapter and level shifter chip were used to connect the computer to the PIC. In this lab, we used a cheap cable found at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220199148938&ih=012&category=41995&ssPageName=WDVW&rd=1
**Important! DO NOT connect the serial Rx/Tx lines DIRECTLY to the PIC!!!**
A level shifter chip is necessary to convert the high and low logic voltages from the desktop computer (+12V/-5V) to (+5V,0V) for the PIC. A standard RS232 connection is called a DB9 connector and follows the pin diagram shown here: http://www.aggsoft.com/rs232-pinout-cable/serial-cable-connections.htmThis cable requires 1 driver installation as included on the mini-cd. To install this driver, you must first plug in the USB cable, and run the installation program located on the CD corresponding to the model on the USB Cable (<CDROM>:HL-232-340HL-340.exe). This driver is also available online at this link: http://129.105.69.13/pic/usb_drivers/HL-340_USB_serial_drivers_WinXP/ . To configure the Matlab script to connect to the proper serial port, use the device manager (Right click My Computer->manage) and expand the section 'Ports (COM & LPT)'. Make a note of the COM port number corresponding to 'USB-SERIAL CH340' as listed in this section. In our program, our serial port was COM4. A picture is shown below of how to get this information in the device manager.
S = serialport, without arguments, connects to the serial port using the property settings of your last cleared serialport object instance. The retained properties are Port, BaudRate, ByteOrder, FlowControl, StopBits, DataBits, Parity, Timeout, and Terminator. The list includes virtual serial ports provided by USB-to-serial devices and Bluetooth ® Serial Port Profile devices. The list shows all the serial ports you can access on your computer and can use for serial port communication. Out = instrfindall finds all serial port objects, regardless of the value of the object’s ObjectVisibility property. The object or objects are returned to out. Out = instrfindall('P1',V1. Run the command by entering it in the MATLAB Command Window.
A female DB9 connector was wired to our level shifter to convert the voltages, with the level shifter connected to our PIC. The female DB9 connector is used so no wires need to be directly soldered to the serial cable. Refer to the Circuit section for details on this connection.
The PIC was programmed with our C code as shown below. Our program was designed to read a potentiometer through the PIC's ADC (Analog to Digital Converter) port and transmit the digitized readings over the serial cable to the PC (upon request). In Matlab, if a users sends data to the PIC by entering a character, the PIC responds with the current potentiometer reading and the last received byte from the PC. The PIC is also programmed to display the character received from the PC on its LED array (D register) as a 8-bit ASCII number. The programs can easily be modified to create any custom protocol, but are designed to show simple 2-way communication between Matlab and the PIC.
Circuit
The serial port object behaves according to the previously configured or default property values. Disconnect and clean up — When you no longer need the serial port object, remove it from the MATLAB ® workspace using the clear command. The serial port session comprises all the steps you are likely to take when communicating with a device connected to a serial port. These steps are: These steps are: Find your serial ports — Display a list of serial ports on your system using the seriallist function.
The wiring diagram for serial communication is shown below. There are three basic components in this setup. The potentiometer serves as an analog input to the PIC, which is converted to a digital signal through the PIC's analog to digital converter pin. The MAX232N level converter provides bidirectional voltage shifting for digital communication between the PIC and PC (read more about this chip and level conversion on the RS232 wiki here). Finally, the female DB-9 connector allows the circuit to connect to the PC's serial port.
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Ziphone for pc. The connections to the female DB-9 adapter are shown below. These wires are soldered to the cup-side of the adapter, not directly to the serial cable. Our DB-9 adapter is pictured below and follows the given connections:
Our final circuit is pictured below.
PIC Code
Tips on Designing a Protocol
A good way to start or debug your program is to use the PIC-C Serial Port Monitor (Tools Tab->Serial Port Monitor). This will allow you to send and receive raw data over the serial port, which is much easier for understanding why a protocol isn't behaving correctly. You can also use HyperTerminal on windows XP (Start->Programs->Accessories->Communications->HyperTerminal), although in our testing this appeared to be less stable than the PIC-C Compiler's monitor. Note for both programs, you will have to configure which serial port to monitor using the same method described in the Overview.
Be sure to close all other programs accessing the serial ports (PIC-C/Hypterm etc.) if you are having difficulty opening the port in MATLAB.
Matlab Code
**** THIS MATLAB CODE SHOULD BE UPDATED TO USE 'fread(s,1)' instead of 'fscanf(s)'. fread(s,1) reads 1 bitwise value at a time (opposed to an ascii value). Without this change, matlab can only read 8 bit ASCII characters and will reject a subset of the values between 0 and 255. *****
If your program doesn't close and delete the serial port object correctly, you can use the command shown below to delete all of the serial port objects.
Matlab List Serial Portsmouth
External Links
Matlab List Available Serial Ports
More on Serial and the PIC: http://hades.mech.northwestern.edu/wiki/index.php/PIC_RS232
MAX232 Data Sheet: http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/MAX232,232I.pdf
Matlab Serial Port Example
Overview of RS232 Protocol: http://en.wikipedia.org/wiki/RS-232