Page 423 - Programming Microcontrollers in C

408 Chapter 8 MCORE, A RISC Machine

#define CLOCK_FREQ 32000000L

/* Initialize the UART1 */
void inituart(int baud)
{
/* Parity is disabled at reset by default */
/* stop bits is set to 1 by default */
/* assumes a 32 mHz system clock */
U1CR1.UARTEN=ON; /* Turn the uart on */
U1CR1.TXEN=ON; /* enable transmitter and receiver */
U1CR1.RXEN=ON;
U1CR2.IRTS=ON; /* ignore request to send */
U1CR2.WS=ON; /* 8 bit word */
/* Baud rate=CLOCK_FREQ/16/baud= */
U1BRGR.CD=(UHWORD)(CLOCK_FREQ/16/baud);
U1PCR.PC3=ON; /* connect all i/o pins to the uarts */
U1PCR.PC2=ON;
U1PCR.PC1=ON;
U1PCR.PC0=ON;
U1DDR.PDC1=ON; /* make output pin for the uart */
}
Listing 8-6: The inituart() Function
Each of these functions will have the same three header functions
shown in Listing 8-6. In this case, the function requires the clock
speed of the chip. This speed can be anything, and in our particular
case, it is 32 MHz. The macro definition CLOCK_FREQ makes this
value 32000000. If you ever change the clock speed of the computer,
this value should be changed. The several instructions in the function
are all commented with their operations. This function should be
executed whenever the serial I/O system is to be used by a program.
Pass the desired baud rate to the function as an integer. The integer
size on the DIAB compiler used for this system is 32 bits; therefore,
there will be no overflow problem for any of the usual choices for
baud rates.
Following the inituart() function above, there is the series
of five functions shown in Listing 8-7. These functions are all placed
together because they each access on-board features of the MCORE
chip. Almost always, it is best to collect operations that access on-
board registers that control peripheral devices into individual functions
that can be called from the applications portion of the program. This
way, the detailed features of the chip are tightly contained in functions