Nuts & Volts - May 2007

THE DESIGN CYCLE

DOES IT REALLY WORK?

I sincerely hope that there was absolutely no doubt in your mind. The Configuration Wizard 2 application can do many wonderful things. However, it can’t write your core application code for you. We went to a bunch of trouble to configure our C8051F120 hardware to spit some ASCII characters out of the UART0 transmit pin. So, I’ve put together a very simple application that sends a message via the UART0 transmit pin and toggles an LED every time the message is sent. Here’s the application code behind my madness:

C statement. I rest my case with Figure 7.

WHERE’S THE HARDWARE?

*********************************************************
void main()
{

unsigned int x,y;    // declare local variables
Init_Device();       // init the microcontroller
SFRPAGE = UART0_PAGE; // enable UART0 access
while(1){
  x = 0xFFFF;
  y = 0x007F;
  do{               // kill some time
    while(—x);
  }while(—y);

// init the kill-time values

  LED = ~LED;       // toggled the LED on P1.6
  printf(“\r\nNUTS AND VOLTS READERS ROCK!\r\n”);
}

}
*********************************************************

Again, no rocket science here. After declaring a couple of integers for use by a kill-time routine, my little C8051F120 application calls the Init_Device function.

Recall that the Init_Device function does everything necessary to prepare the C8051F120 peripherals and general-purpose I/O pins for pumping stuff out of UART0 and bit twiddling the LED, which is attached to general-purpose I/O pin P1.6. I selected the kill-time delay values to toggle the LED and send a message once every couple of seconds.

Sending a message using UART0 involves writing to the UART0 buffer register SBUF0. We must load the SFRPAGE register with the SBUF0 SFR page so we can address the SBUF0 register within the SBUB0 SFR page. The kill-time routine is a simple do-while loop that decrements the x variable from 0xFFFF to zero as long as the y variable has not decremented to zero itself. When all of the integer variables expire to zero, the LED is toggled and a message is emitted from UART0. This is all contained within the braces of an endless loop created by the while(1)

(Yes, I was tempted to headline this section as “Where’s the Beef?”) If you’ve ever taken pilot training, you know that more time is spent on the ground in training than in the air when you begin the process. With that thought, you’ve done enough ground training with the C8051F120, and in the next installment of Design Cycle, we’ll jump into the cockpit of a C8051F120 microcontroller. In addition to examining the C8051F120 hardware, we’ll finish off writing some code for the rest of the C8051F120 peripherals. In the meantime, I’ll post the C source code and the Configuration Wizard 2 configuration file (nuts_and_volts.cwg) we discussed here on the Nuts & Volts website for you.

For those of you that want to get your hands dirty right now, you’ll need to get a demo or registered copy of the Keil C51 C Compiler and a Silicon Laboratories USB Debug Adapter to run the code I’ve presented in this Design Cycle entry. The easy way to do this is to get yourself a Silicon Laboratories C8051F120 Development Kit, which contains a nifty C8051F120- equipped development board, a demo version of the Keil C51 C Compiler, and a Silicon Laboratories USB Debug Adapter. I’ll show you how to integrate and use the Keil and Silicon Laboratories tools as we put the C8051F120 hardware through its paces next time around. NV

CONTACTING THE AUTHOR

■ Peter Bestcanbereachedviaemailatpeter@nerdvilla.com.

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