sfr16 TMR2RL = 0xca; // Timer2 reload value
sfr16 TMR2 = 0xcc; // Timer2 counter
#define SYSCLK 12000000 / 8 // SYSCLK frequency in Hz
#define BLINK_RATE 10 // Timer2 Interrupts per second
sbit LED1 = P2^2; // LED='1' means ON
void OSCILLATOR_Init (void);
void PORT_Init (void);
void Timer2_Init (int counts);
void Timer2_ISR (void)
void main (void)
{
PCA0MD &= ~0x40; // WDTE = 0 (clear watchdog timer
// enable)
OSCILLATOR_Init (); // Initialize system clock
PORT_Init (); // Initialize crossbar and GPIO
Timer2_Init (SYSCLK / 12 / BLINK_RATE); // Init Timer2 to generate
// interrupts at a 10Hz rate
EA = 1; // Enable global interrupts
while (1) {} // Spin forever
}
void OSCILLATOR_Init (void)
{
OSCICN = 0x80; // Configure internal oscillator for
// its lowest frequency)
}
void PORT_Init (void)
{
XBR0 = 0x00; // No digital peripherals selected
XBR1 = 0x40; // Enable crossbar and weak pull-ups
P2MDOUT |= 0x04; // Enable LED as a push-pull output
}
void Timer2_Init (int counts)
{
TMR2CN = 0x00; // Stop Timer2; Clear TF2
// Use SYSCLK/12 as timebase
CKCON &= ~0x60; // Timer2 clocked based on T2XCLK
TMR2RL =-counts; // Init reload values,
TMR2 = 0xffff; // Set to reload immediately
ET2 = 1; // Enable Timer2 interrupts
TR2 = 1; // Start Timer2
}
void Timer2_ISR (void) interrupt 5
{
TF2H = 0; // Clear Timer2 interrupt flag
LED1 = ~LED1; // Change state of LED
}
这个是silicon labs IDE安装后的一个例子程序,功能是要实现开发板上的发光二级管在一秒内大约闪5次,小弟对
TMR2RL =-counts; // Init reload values
这行代码中-counts没看懂,counts前面的那个-是什么意思?赋计数初值不就是count吗?怎么前面还有个“-”呢?我试了下,如果counts前面有“-”的话,二极管可以在一秒内大约闪5次,如果把前面的“-”去掉的话,二极管大约1秒闪一次那样(没仔细数,总之等比原来闪频率要慢很多),求大神给小弟指点下,那个“-”是什么意思?