Page 232 - Programming Microcontrollers in C

Header File 217

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PORTA.MOTOR = ON; /* turn the motor on */
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if(PORTA.PUSH_BUTTON==ON)
{
do push button things
}

With this compiler, an int is a 16-bit value. Therefore, the
registers that are two bytes are cast onto the type int. Usually these
registers are accessed as ints only and there is no need to have the
individual bit access afforded by the use of the Register type.
The timer counter register (TCNT) is one such register that is accessed
as an int only. There are also a few one byte, or 8-bit, registers that
are accessed as bytes only. No bit accesses within these registers are
needed. In these cases, the register is cast onto the type char. The
several ADRx registers are examples of this type. The ADRx registers
contain the result of an analog-to-digital conversion that is usually
handled as an 8-bit unit only.
In most instances, register locations should be unsigned. The ADRx
registers each contain the result of analog-to-digital conversions. These
results are all unsigned. Therefore, these registers should be cast as
unsignedchar. Also note that all of the timer count and input capture
or output compare registers are also declared as unsigned.
In the listing above, you will note that there are two parts to the
declaration of each register. The first identifies all of the bits in the
register through a structure typedef. Then a macro definition of the
port name causes each instance of the port name in the program to be
replaced by the dereferenced value of the register address cast onto a
pointer of the correct type. The port name is the name of the port
found in the data manual, and the bit names given the bits in the structure
are the names found in the data manual. Therefore, if you wish to set
the bit named HNDS found in the register PIOC, you need to use

PIOC.HDNS=ON;
There are two register locations that work differently from the
rest. These are the two flag registers whose bits are set by the