Page 292 - Programming Microcontrollers in C

Timer Operations 277

bits, transmit enable and receive enable, that must be set to enable
the SCI. The following two lines of code will enable these bits.
SCCR2.TE=1;
SCCR2.RE=1;

These two lines of code must also be added to the initialization portion
of the program.
The code to read the data in is as follows:

if (SCCR.RDRF==1) /* read in data if it is there */
{
new_character=SCDR;/*get new byte and reset RDRF*/
while(SCCR.TDRE==0); /* wait until transmit
buffer empty */
SCDR=new_character; /* send out byte and reset
TDRE */
}

This sequence of code does quite a bit more than you might expect.
Before this code sequence can be executed, both the RDRF and TDRE
flags must be set and reset. The RDRF is set when a character has
been received by the SCI, and the TDRE is set when the SCDR is
empty and can receive a character to send. Both of these bits are reset
by the sequential read of SCSR with the bit set followed by a read for
the RDRF or a write for the TDRE to the SCDR register. The above
sequence accomplishes all of the proper bit resets, transmits the newly
received character back to the sender, and leaves the new character
in the location new_character . After receiving the data, the
following sequence converts it into a binary number to be processed
by the remainder of the program.
if (SCSR.RDRF==1) /* read in data if there */
{
new_character=SCDR;/*get new byte and reset RDRF*/
while(SCSR.TDRE==0); /* wait until transmit
buffer empty */
SCDR=new_character; /* send out byte and reset
TDRE */
/* if a number, process it */
if(new_character>=’0' && new_character <=’9')