Programming Embedded Systems in C and C++

Study the External Peripherals 53

#define P1DIR (PCB_BASE + 0x50)

#define P1PIN (PCB_BASE + 0x52)

#define P1CON (PCB_BASE + 0x54)

#define P1LTCH (PCB_BASE + 0x56)

#define P2DIR (PCB_BASE + 0x58)

#define P2PIN (PCB_BASE + 0x5A)

#define P2CON (PCB_BASE + 0x5C)

#define P2LTCH (PCB_BASE + 0x5E)

Other things you’ll want to learn about the processor from its databook are:

• Where should the interrupt vector table be located? Does it have to be located

at a specific address in memory? If not, how does the processor know where

to find it?

• What is the format of the interrupt vector table? Is it just a table of pointers to

ISR functions?

• Are there any special interrupts, sometimes called traps, that are generated

within the processor itself? Must an ISR be written to handle each of these?

• How are interrupts enabled and disabled (globally and individually)?

• How are interrupts acknowledged or cleared?

Study the External Peripherals

At this point, you’ve studied every aspect of the new hardware except the exter-

nal peripherals. These are the hardware devices that reside outside the processor

chip and communicate with it by way of interrupts and I/O or memory-mapped

registers.

Begin by making a list of the external peripherals. Depending on your applica-

tion, this list might include LCD or keyboard controllers, A/D converters, network

interface chips, or custom ASICs (Application-Specific Integrated Circuits). ...