Nuts and Volts - January 2009

THE SOFTWARE AND HOW IT WORKS

The software is fairly simple and is shown in Listing 1. The program initially sets up the control registers in the PIC16F690. PortC is made into an output and then initially set to all zeros. The PIC16F690 defaults to analog-pin mode, so the pins have to be made digital by clearing the ANSEL register. The internal comparators are turned off by clearing their respective registers.

control byte. The control byte for the 24LC01B is in the datasheet and is (binary) %1010xxx, where xxx is the setting for the A0, A1, and A2 pins of the EEPROM. You can have more than one EEPROM connected to the I C

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bus, so setting those pins to something other than ground allows you to create a new control byte for that particular part. If we had a second EEPROM hooked up to the bus, its control byte could be %1010001. This would require the A0 pin to be pulled to VDD instead of ground.

TRISC = 0

PORTC = 0

ANSEL = 0

CM1CON0 = 0

CM2CON0 = 0

A few constants and variables are created. The serial communication pin is PORTC.0, which is also pin 8 in the PICBASIC PRO PIC16F690 setup. The PICkit 2 acts as a true UART hardware interface, even though it sends the data back to the USB port. Therefore, we need the True mode — or T2400 — for 2400 baud communication. The N2400 is there just to work with a direct connection to another PIC MCU instead of a PC.

For B0 = 0 To 15 ' Loop 16 times
  I2CWRITE DPIN,CPIN,$A0,B0,[B0] ' Write each
 ' location's
 ' address to
 ' itself
 Pause 10 ' Delay 10ms
 ' after each
 ' write

Next B0

SO
N2400
T2400
DPIN
CPIN
B0
B1

con
con
CON
var
var
var
var

8
4
0
PORTA.2 ' I2C data pin
PORTA.1 ' I2C clock pin
byte ' Temporary Byte
byte ' Temporary Byte

' Define serial output pin
' Set serial mode

Here is another example of why I like the PICBASIC PRO compiler for the beginning programmer. The compiler has I2CWRITE and I2CREAD commands to make this very easy. The commands can use any digital port since they "bit-bang" the I C signal. The command handles all the

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timing and reading of the ACK bits. It also handles the read or write bit in the control byte. The only things you need to supply in the command line are the connection designation for the data and clock pins, plus the

The program just “For-Loops” through setting each memory address to the same value as the address (i.e., address 0 has data value 0; address 1 has data value 1, etc.). This creates the initial data in the EEPROM. Next, another For-Loop reads each address and sends the data read to the PICkit 2 UART screen using the SEROUT command. Figure 4 shows the UART screen and the 16 address locations read back from the EEPROM. The "#" symbol in front of the B1 variable converts the decimal value into an ASCII value for the UART. In other words, a value of 15 is sent as two bytes — an ASCII "1" and ASCII " 5" so it is displayed as 15, rather than the ASCII character associated with decimal 15.

Figure 5 shows the MPLAB IDE window complete with the PICkit 2 running. You need MPLAB IDE v. 8. 14

or later to use two PICkit 2 programmers at the same time; otherwise, the software won't know which one goes to the MPLAB IDE and which one goes to the UART. The MPLAB IDE software or the PICkit 2 GUI will first ask which PICkit 2 you want to connect to. I've covered how you can store a unique name inside the PICkit 2's memory to make it easier to select the correct programmer in past articles. Check the PICkit 2 manual for instructions on how to "set the unit ID." The UART software is under the tool menu of the PICkit 2 standalone GUI software that comes with the programmer. Both the MPLAB IDE and PICkit 2 software can be downloaded from Microchip's website