Part 4: Serial, Sonar and Servos Continued

In Bascom, one method of sending serial data is the PRINT command. To send the string "Hello World" to the other microcontroller the command is:

PRINT "Hello World"

To receive serial data, the INPUT or INKEY commands are used. INPUT is used to receive a line of data that is terminated with a line feed character. INKEY is used to receive characters one at a time.  Our program uses the INKEY command to receive data.

Byterecvd = INKEY()

Byterecvd has the value 0 (zero) if no character was received. If a character was received, Byterecvd contains the ASCII code.

The speed that serial data is sent & received is called the BAUD rate. We are using 9600 but you can use faster or slower speeds to suit your need.

Let's look at the Primary Serial Test Code (an underscore at the end of a line means the text wraps to the next line):

'CIRCBot Primary MCU Serial Test Code
'Load into the lower Mega48
$regfile = "m48def.dat"
$baud = 9600
$crystal = 8000000
$hwstack = 32
$swstack = 32
$framesize = 32

The statements above tells the compiler (Bascom) important information about the microcontroller - which chip, what frequency and what baud rate. HWStack, SWTack and Framesize are memory buffers used by the compiler.  All of these settings are accessible through the Options menu. But by putting these statements in your program, anyone looking at your code will know what the correct settings are.

Dim Char As String * 1 , Mystr As String * 16 , Byterecvd As Byte
Dim Dist As Byte , Count As Byte , Timeout As Word

The DIM statements define or dimension the variables we are using in the program.

Config Lcdpin = Pin , Db4 = Portc.0 , Db5 = Portc.1 , Db6 = Portc.2 , Db7 = Portc.3 , E = Portd.4 , Rs_ = Portd.3
Config Lcd = 16 * 1a 'Type of LCD Display

These two lines configure the LCD display.  If you have a 16x2 display, change the second line to read "16 * 2". For a 20x4 display, change it to "20 * 4".

Cls 'Clear the LCD Display
Cursor Off 'Turn off the Blinking Cursor
Wait 1
Lcd "Starting..."
Wait 5

The CLS command clears the LCD and puts the cursor in home position, at the beginning of the line. Cursor Off command removes the blinking cursor from the LCD display. The Wait statement cause the program to pause for the number of seconds specified.  The LCD command prints the text on the LCD display, similar to the Print command used to send data out the serial port.

Enable Interrupts

Enable Interrupts is a global flag for the microcontroller, enabling all interrupts. Think of it as a master on/off switch for interrupts.

Count = 1
Timeout = 0
Do
   Timeout = 0
   If Count = 1 Then Print "100" 'This number represents pointing straight ahead
   If Count = 2 Then Print "65" 'This number represents pointing right
   If Count = 3 Then Print "135" 'This number represents pointing left

The If statements allow us to send different messages based on the value of Count. When Count = 1 is true, the IF statement will execute the Print statement that follows Then.

   Mystr = ""
   Do
      Byterecvd = Inkey() 'Look for data sent back to us

As we discussed above, the Inkey statement is used to look for data coming from the serial port. When no data is available, Inkey returns a zero value.

      Select Case Byterecvd 'Decide what to do based on the value of Byterecvd

      Case 0
      'No data available
      Incr Timeout
      Waitms 1
      If Timeout > 500 Then
         Timeout = 0
         Dist = 0
         Exit Do
      End If

      Case 10
      'Linefeed, got our data
      Timeout = 0
      Dist = Val(mystr)
      Exit Do

      Case 13
      'Carriage Return, ignore
      Timeout = 0

      Case Else
      Char = Chr(byterecvd) 'Convert the Data into a string
      Mystr = Mystr + Char '
      Timeout = 0

      End Select

The Select Case statement lets us run blocks of code based on the value of a variable - Byterecvd in this case. As the text data is received, each byte is checked using the Select Case statement above. There are three special values that we want to handle differently than the rest:

0 (zero) - No data present, increment a timeout value so we don't get stuck in an endless loop here
13 - Carriage Return. each text message ends with a Carriage Return character and a Line Feed character. The Carriage Return character isn't used but we don't want it appended to the string variable. By calling it out separately, no action is taken when Carriage Return is detected.
10 - Line Feed.  This character represents the end of a text message. This tells us to stop looking for characters and process the message we received.

   Loop
   Cls 'Clear the LCD
   Lcd "DIST: " ; Dist
   Wait 2
   Incr Count
   If Count > 3 Then Count = 1

Loop

When Line Feed is detected, it causes the program to exit the loop via the Exit Do command. The command following Loop is executed next, in this case it is CLS.  The LCD command is used to display the message we received from the Secondary microcontroller. The message is the distance detected by the Sonar Sensor.

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