Saif Ullah Qureshi, Lahore, Pakistan
1.d 8051 Family:
1.f Timers /Counter:
Counter/timer hardware is a crucial component of most embedded systems. In some cases, a timer measures elapsed time (counting processor clock ticks). In others, we want to count or time external events. The names counter and timer can be used interchangeably when talking about the hardware. The difference in terminology has more to do with how the hardware is used in a given application.
1.e Intterupt Control:
· Two external interrupts (INT0 and INT1.
· Two timer interrupts (timer 0 and timer 1)
· One serial port receive interrupt.
· One serial port transmit interrupt
Each interrupt is assigned a ®xed location in memory and an interrupt causes the CPU to jump to that location, where it executes the interrupt service routine. Table 1.5 gives the interrupt sources and the start of their service routines in memory. Note that the serial port receives and transmit interrupts point to the same location. Each interrupt source can be individually enabled or disabled by setting or clearing its interrupt enable bit. Table 1.6 gives the interrupt enable bit patterns.