Page 273 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 06 3/24/03 9:02 AM Page 252
Amphibionics
When using the serin command to receive data, PicBasic Pro lets
you define a qualifier enclosed within brackets before any more
data is received. Serin must receive these bytes in exact order
before receiving any data items. If any bytes received do not match
the next byte in the qualifier sequence, the qualification process
starts over (i.e., the next received byte is compared to the first item
in the qualifier list). This makes it easy for us to program an iden-
tification code for each device or robot that we are going to con-
trol. It also ensures that good data are being sent, and cuts down
on erroneous interpretation of the received serial data. Once the
qualifiers are satisfied, serin begins storing data in the variables
associated with each item. If the variable name is used alone, the
value of the received ASCII character is stored in the variable.

For our test program, we will use the qualifier “Z” to identify that
the received data is coming from our transmitter. Once the char-
acter “Z” has been received, the next byte of information will be
stored in a variable. We can then compare this information to cer-
tain control commands and carry out the tasks associated to them.
The line of code that will receive the serial data looks like this:

serin rxmit,rx_baud,["Z"],control

The serial data is received on pin rxmit (PORTB.0) at a baud rate
of rx_baud (2400). The program execution will remain in a tight
loop, receiving serial data and comparing each received byte to the
character “Z.” When the character “Z” is received, the next data
byte is stored in the variable named control. We will then compare
the contents of the variable control to the character “A.” If the
comparison is true, then the microcontroller will produce a couple
of tones on the piezo speaker. The receiver program is called
receive-test.bas and is listed in Program 6.7. Program the PIC
16F84 with the receive-test.hex file listed in Program 6.8. Place
the PIC in the 18-pin socket on the robot’s main board.

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