Page 322 - Programming Microcontrollers in C

Cosmic MC68HC16 Compiler 307

;
.end
In the above code, the EK, XK, and ZK registers are initialized
to the value found in .__bss__ . The initial value of YK is set to
0xf. The Y register will be used by the compiler to contain an offset
to all of the data contained in the control registers found in the header
files. Therefore, the YK register must be set to the top memory block
in the computer memory space.

Using the SCI Portion of the Queued Serial Module
The queued serial module (QSM) contains two parts. The first is a
convenient serial communications interface (SCI) which provides
asynchronous serial communications that is used between comput­
ers and other devices. The remainder of the QSM is a queued serial
peripheral interface that is often used for high-speed communica­
tions between computers and peripheral devices. This interface is
strictly synchronous.
Let’s examine an interface between the program and a terminal
much like that found in Chapter 5. Here, the interface will simply
read in a number from the screen and put that number into the
pwm_count value for the PWM program. With this operation in
place, the operator can type in a value and change the PWM on time
at will. Listing 6-3 contains a program that will accomplish this end.
#include “hc16.h”
#include “gpt.h”
#include “sim.h”
#include “qsm.h”
#include “defines.h”

#define PERIOD 0x1000
#define ON_TIME 0x0800
#define SIM_IARB 4
#define GPT_IARB 10
#define GPT_IRL 6
#define GPT_VBA 5
/* set the baud rate=fclock/32*baud_rate */
#define BAUD_SET (32768*512)/(32*38400)

/* function prototypes */
@port void OC3_Isr(void);