1. Example 13 The Serial Peripheral Interface (SPI)
Lecture L9.1

2. PIM_9DP256
Block Diagram
3 SPI Ports

3. SPI2 Pins
PP4 – PP7
Pins 112,111,110,109
SPI1 Pins
PP0 – PP3
Pins 4,3,2,1
SPI0 Pins
PS4 – PS7
Pins 93,94,95,96

4. SPI2 Pins
PP4 – PP7
Pins 112,111,110,109
SPI1 Pins
PP0 – PP3
Pins 4,3,2,1
SPI0 Pins
PS4 – PS7
Pins 93,94,95,96

6. Two SPI modules connected in a master-slave configuration

7. $D8

11. Connecting a 16 x 1 hex keypad to two 74165 shift registers

12. int read_16shift(void){
int data;
char c;
SS0_LO(); // latch data
SS0_HI();
c = send_SPI0(0); // get 1st byte by sending dummy data
data = c;
data = data << 8;
c = send_SPI0(0); // get 2nd byte by sending dummy data
data = data | c;
return data; }

13. char get_key(){
const char keytbl[] = {
0x3, 0x2, 0x1, 0x0,
0x8, 0x9, 0xA, 0xB,
0x7, 0x6, 0x5, 0x4,
0xC, 0xD, 0xE, 0xF };
int mask;
int data;
int i;
char found;
char key;
data = read_16shift();
mask = 0x8000;
found = 0;
i = 0;
key = 16; // not found if key = 16
while((i < 16) && (found == 0)){
if((data & mask) == 0){
found = 1;
key = keytbl[i]; }
else {
mask >>= 1;
i++;
return key;

14. // Example 13: SPI Keypad Interfacing with 74165 Shift Registers
#include <hidef.h> /* common defines and macros */
#include <mc9s12dp256.h> /* derivative information */
#include "main_asm.h" /* interface to the assembly module */
#pragma LINK_INFO DERIVATIVE "mc9s12dp256b"
int read_16shift(void);
char get_key(void);
void main(void) {
char key;
PLL_init(); // set system clock frequency to 24 MHz
lcd_init(); // enable lcd
SPI0_init(); // enable SPI0
set_lcd_addr(0x40);
while(1) {
key = get_key();
if(key < 16){
key = hex2asc(key); // convert to ascii
data8(key); // display on lcd }