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Example_Touchpads/Touchpad_3p2.ino
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// This software is in the public domain
// It interfaces the Teensy 3.2 with a PS/2 touchpad found in a laptop.
// The PS/2 code was originally from https://playground.arduino.cc/uploads/ComponentLib/mouse.txt
// but the interface to the PC was changed from RS232 serial to USB using the PJRC Mouse functions.
// A watchdog timer was also added to the "while loops" so the code doesn't hang if the touchpad hiccups.
//
// This code has been tested on the touchpad from an HP Pavilion DV9000
// Touchpad part number 920-000702-04 Rev A
// The test points on the touchpad were wired to a Teensy 3.2 as follows:
// T22 = 5V wired to the Teensy Vin pin
// T23 = Gnd wired to the Teensy Ground pin It's hard to solder to T23 so I soldered to a bypass cap gnd pad.1
// T10 = Clock wired to the Teensy I/O 14 pin
// T11 = Data wired to the Teensy I/O 15 pin
//
// Clock and Data measure open to the 5 volt pin, indicating no pull up resistors but,
// Clock and Data both measure 5 volts when the touchpad is powered, indicating active pullups are in
// the touchpad blob top chip.
// The ps/2 signals are at 5 volts from the touchpad to the Teensy which is 5 volt tolerant.
// The ps/2 signals are at 3.3 volts from the Teensy to the touchpad which is enough to be a logic high.
//
// Revision History
// Initial Release Oct 16, 2018
//
// The touchpad ps/2 data and clock lines are connected to the following Teensy I/O pins
#define MDATA 15
#define MCLK 14
//
// Declare variable that will be used by functions
boolean touchpad_error = LOW; // sent high when touch pad routine times out
//
// Function to float a pin and let the pull-up or Touchpad determine the logic level
void go_z(int pin)
{
pinMode(pin, INPUT); // make the pin an input so it floats
digitalWrite(pin, HIGH);
}
// function to drive a pin to a logic low
void go_0(int pin)
{
pinMode(pin, OUTPUT);
digitalWrite(pin, LOW);
}
// Function to send the Touchpad a command
void touchpad_write(char data)
{
char i;
char parity = 1;
// put pins in output mode
go_z(MDATA);
go_z(MCLK);
elapsedMillis watchdog; // set watchdog to zero
delayMicroseconds(300);
go_0(MCLK);
delayMicroseconds(300);
go_0(MDATA);
delayMicroseconds(10);
// start bit
go_z(MCLK);
// wait for touchpad to take control of clock)
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// clock is low, and we are clear to send data
for (i=0; i < 8; i++) {
if (data & 0x01) {
go_z(MDATA);
}
else {
go_0(MDATA);
}
// wait for clock cycle
while (digitalRead(MCLK) == LOW) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
parity = parity ^ (data & 0x01);
data = data >> 1;
}
// parity
if (parity) {
go_z(MDATA);
}
else {
go_0(MDATA);
}
// wait for clock cycle
while (digitalRead(MCLK) == LOW) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// stop bit
go_z(MDATA);
delayMicroseconds(50);
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// wait for touchpad to switch modes
while ((digitalRead(MCLK) == LOW) || (digitalRead(MDATA) == LOW)) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// put a hold on the incoming data.
go_0(MCLK);
}
//
// Function to get a byte of data from the touchpad
//
char touchpad_read(void)
{
char data = 0x00;
int i;
char bity = 0x01;
// start the clock
elapsedMillis watchdog; // set watchdog to zero
go_z(MCLK);
go_z(MDATA);
delayMicroseconds(50);
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
delayMicroseconds(5); // wait for clock ring to settle
while (digitalRead(MCLK) == LOW) { // eat start bit
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
for (i=0; i < 8; i++) {
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
if (digitalRead(MDATA) == HIGH) {
data = data | bity;
}
while (digitalRead(MCLK) == LOW) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
bity = bity << 1;
}
// ignore parity bit
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
while (digitalRead(MCLK) == LOW) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// eat stop bit
while (digitalRead(MCLK) == HIGH) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
while (digitalRead(MCLK) == LOW) {
if (watchdog >= 200) { //check for infinite loop
touchpad_error = HIGH; // set error flag
break;
}
}
// put a hold on the incoming data.
go_0(MCLK);
return data;
}
void touchpad_init()
{
touchpad_error = LOW; // start with no error
go_z(MCLK); // float the clock and data to touchpad
go_z(MDATA);
// Sending reset to touchpad
touchpad_write(0xff);
touchpad_read(); // ack byte
// Read ack byte
touchpad_read(); // blank
touchpad_read(); // blank
// Default resolution is 4 counts/mm which is too small
// Sending resolution command
touchpad_write(0xe8);
touchpad_read(); // ack byte
touchpad_write(0x03); // value of 03 gives 8 counts/mm resolution
touchpad_read(); // ack byte
// Sending remote mode code so the touchpad will send data only when polled
touchpad_write(0xf0); // remote mode
touchpad_read(); // Read ack byte
delayMicroseconds(100);
}
// ************************************Begin Routine*********************************************************
void setup()
{
touchpad_init(); // reset touchpad, then set it's resolution and put it in remote mode
if (touchpad_error) {
touchpad_init(); // try one more time to initialize the touchpad
}
}
// declare and initialize variables
char mstat; // touchpad status reg = Y overflow, X overflow, Y sign bit, X sign bit, Always 1, Middle Btn, Right Btn, Left Btn
char mx; // touchpad x movement = 8 data bits. The sign bit is in the status register to
// make a 9 bit 2's complement value. Left to right on the touchpad gives a positive value.
char my; // touchpad y movement also 8 bits plus sign. Touchpad movement away from the user gives a positive value.
boolean over_flow; // set if x or y movement values are bad due to overflow
boolean left_button = 0; // on/off variable for left button = bit 0 of mstat
boolean right_button = 0; // on/off variable for right button = bit 1 of mstat
boolean old_left_button = 0; // on/off variable for left button status the previous polling cycle
boolean old_right_button = 0; // on/off variable for right button status the previous polling cycle
boolean button_change = 0; // Active high, shows when a touchpad left or right button has changed since last polling cycle
// ************************************Main Loop***************************************************************
void loop() {
// poll the touchpad for new movement data
over_flow = 0; // assume no overflow until status is received
touchpad_error = LOW; // start with no error
touchpad_write(0xeb); // request data
touchpad_read(); // ignore ack
mstat = touchpad_read(); // save into status variable
mx = touchpad_read(); // save into x variable
my = touchpad_read(); // save into y variable
if (((0x80 & mstat) == 0x80) || ((0x40 & mstat) == 0x40)) { // x or y overflow bits set?
over_flow = 1; // set the overflow flag
}
// change the x data from 9 bit to 8 bit 2's complement
mx = mx >> 1; // convert to 7 bits of data by dividing by 2
mx = mx & 0x7f; // don't allow sign extension
if ((0x10 & mstat) == 0x10) { // move the sign into
mx = 0x80 | mx; // the 8th bit position
}
// change the y data from 9 bit to 8 bit 2's complement and then take the 2's complement
// because y movement on ps/2 format is opposite of touchpad.move function
my = my >> 1; // convert to 7 bits of data by dividing by 2
my = my & 0x7f; // don't allow sign extension
if ((0x20 & mstat) == 0x20) { // move the sign into
my = 0x80 | my; // the 8th bit position
}
my = (~my + 0x01); // change the sign of y data by taking the 2's complement (invert and add 1)
// zero out mx and my if over_flow or touchpad_error is set
if ((over_flow) || (touchpad_error)) {
mx = 0x00; // data is garbage so zero it out
my = 0x00;
}
// send the x and y data back via usb if either one is non-zero
if ((mx != 0x00) || (my != 0x00)) {
Mouse.move(mx,my);
}
//
// send the touchpad left and right button status over usb if no error
if (!touchpad_error) {
if ((0x01 & mstat) == 0x01) { // if left button set
left_button = 1;
}
else { // clear left button
left_button = 0;
}
if ((0x02 & mstat) == 0x02) { // if right button set
right_button = 1;
}
else { // clear right button
right_button = 0;
}
// Determine if the left or right touch pad buttons have changed since last polling cycle
button_change = (left_button ^ old_left_button) | (right_button ^ old_right_button);
// Don't send button status if there's no change since last time.
if (button_change){
Mouse.set_buttons(left_button, 0, right_button); // send button status
}
old_left_button = left_button; // remember new button status for next polling cycle
old_right_button = right_button;
}
//
// **************************************End of touchpad routine***********************************
//
delay(30); // wait 30ms before repeating next polling cycle
}