Page 456 - Programming Microcontrollers in C

Integrating Keyboard and Clock 441

when the ‘1’ button is depressed and the hours increase when the ‘2’
button is depressed. The program will need the interrupt service
routine, but the recording of the data into a buffer and all of the
attendant decoding is unnecessary here. We will use a single global
variable to set when a correct key is depressed. That is all required
for this application.
Let’s start with the initialization routine. This initialization routine
needs to do even less than was needed earlier. Consider the code:
/* key board initialization routine */
void kpinit(void)
{

KPCRN.LOROWS=0xf; /* enable keypad rows */
KPDRB.COLUMNS=0x0; /* write 0 to KPDR[15:8] */
KPCRN.LOCOLS=0xf; /* make cols open drain */
KDDRN.LOCOLS=0xf; /* make cols outputs */
KDDRN.LOROWS=0x0; /* and rows inputs */
KPSR.KPKD=ON; /* clear KPKD status flag */
KPSR.KDSC=ON; /* clear key depress synchronizer */
KPSR.KDIE=ON; /* set KDIE bit to enable depress
Interrupt */
KPSR.KRIE=OFF; /* disable release interrupt */
FIER.EF6=ON; /* enable Fast Interrupt number 6*/
}
The main change observed is that no parameters are passed to the
initialization function and none of the variables saved earlier are
needed here. Otherwise, this function is identical to the earlier
kpinit() function.
The changes made in kb_isr() are instructive. There is no
substantive change in the function until after the depressed key has
been detected. For this program, we are interested only in the detection
of a ‘1’ or a ‘2’. These digits correspond to the position values 0x42
and 0x22 respectively. After the key has been detected, a simple case
statement converts these specific values to the proper digits. If the
position numbers are not one of the expected values, *data is
assigned a value of zero. This value is used by the main() program
to determine when a key has been depressed.

/* key board interrupt service routine */
void kb_isr(void)
{
UHWORD column,input;