Page 434 - Programming Microcontrollers in C

A Clock Program 419

Table 8-2 Interrupt Controller Assignments
Bit
Use
Number
0, 1, 2 Software
3 unused
4 unused
5 UART0 RTS_DELTA
6 KPP control
7 Time-of-day alarm
8 PIT
9 unused
10 PWM0
11 PWM1
12 PWM2
13 PWM3
14 PWM4
15 PWM5
16 UART0 transmit
17 UART1 transmit
18 UART0 receive
19 UART1 receive
20 ISPI
21 INT0
22 INT1
23 INT2
24 INT3
25 INT4
26 INT5
27 INT6
28 INT7
29 unused
30 unused
31 unused

A Clock Program

A clock program is an excellent program for demonstrating the
use of interrupts on a microcontroller. The MMC2001 has a rather
extensive timer subsystem. It is broken into three parts. There is a
time of day clock, TOD, with a built-in alarm, a watchdog timer and
a programmable interval timer, PIT. We will use the PIT in this
example. Briefly, the timers are driven by a separate clock. The clock
here is a 32768-Hz clock controlled by a watch crystal. The TOD