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Example_Touchpads/Touchpad_Stream_mode.ino

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+//
+// This software interfaces a Teensy 3.2 with a PS/2 laptop touchpad.
+// The touchpad is commanded to be in Stream Mode (not remote mode).
+// This causes the touchpad to send data when ever it detects finger movement.
+// The ps/2 code uses the USB PJRC Mouse functions at www.pjrc.com/teensy/td_mouse.html 
+// The ps/2 code has a watchdog timer so the code can't hang if a clock edge is missed.
+// In the Arduino IDE, select Tools, Teensy 3.2. Also under Tools, select Keyboard+Mouse+Joystick
+//
+// Revision History
+// Rev 1.0 - Aug 1, 2020 - Original Release
+//
+// The touchpad ps/2 data and clock lines are connected to the following Teensy I/O pins
+#define TP_DATA 0
+#define TP_CLK 1
+// Teensy LED will be turned ON to show if errors are detected during initialization or during normal use
+#define ERROR_LED 13
+//
+// Declare variables that will be used by functions
+boolean init_error = LOW; // set high if initialization detects an error
+boolean bit_error = LOW; // set high if main loop detects an error
+char mstat; // touchpad status 8 bit register = 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 bit in status reg. Touchpad movement away from the user gives a positive value.
+//
+// Function to set a pin to high impedance (acts like open drain output)
+void go_z(int pin)
+{
+  pinMode(pin, INPUT);
+  digitalWrite(pin, HIGH);
+}
+//
+// Function to set a pin as an input with a pullup
+void go_pu(int pin)
+{
+  pinMode(pin, INPUT_PULLUP);
+  digitalWrite(pin, HIGH);
+}
+//
+// Function to set a pin to a logic low
+void go_0(int pin)
+{
+  pinMode(pin, OUTPUT);
+  digitalWrite(pin, LOW);
+}
+//
+// Function to set a pin to a logic high
+void go_1(int pin)
+{
+  pinMode(pin, OUTPUT);
+  digitalWrite(pin, HIGH);
+}
+//
+// *****************Functions for Touchpad***************************
+//
+// Function to send the touchpad a byte of data (command)
+//
+void tp_write(char send_data)  
+{
+  unsigned int timeout = 200; // breakout of loop if watchdog over this value in msec
+  elapsedMillis watchdog; // zero the watchdog timer clock
+  char odd_parity = 0; // clear parity bit count
+// Enable the PS/2 bus by floating the clock and data
+  go_pu(TP_CLK); //
+  go_pu(TP_DATA); //
+  delayMicroseconds(250); // wait before requesting the bus
+  go_0(TP_CLK); //   Send the Clock line low to request to transmit data
+  delayMicroseconds(100); // wait for 100 microseconds per bus spec
+  go_0(TP_DATA); //  Send the Data line low (the start bit)
+  delayMicroseconds(1); //
+  go_pu(TP_CLK); //   Release the Clock line so it is pulled high
+  delayMicroseconds(1); // give some time to let the clock line go high
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop because tp did not respond
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+// send the 8 bits of send_data 
+  for (int j=0; j<8; j++) {
+    if (send_data & 1) {  //check if lsb is set
+      go_pu(TP_DATA); // send a 1 to TP
+      odd_parity = odd_parity + 1; // keep running total of 1's sent
+    }
+    else {
+      go_0(TP_DATA); // send a 0 to TP
+    }
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+      if (watchdog >= timeout) { //check for infinite loop
+        init_error = HIGH;
+        break; // break out of infinite loop
+      }
+    }
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+      if (watchdog >= timeout) { //check for infinite loop
+        init_error = HIGH;
+        break; // break out of infinite loop
+      }
+    }  
+    send_data = send_data >> 1; // shift data right by 1 to prepare for next loop
+  }
+// send the parity bit
+  if (odd_parity & 1) {  //check if lsb of parity is set
+    go_0(TP_DATA); // already odd so send a 0 to TP
+  }
+  else {
+    go_pu(TP_DATA); // send a 1 to TP to make parity odd
+  }   
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  go_pu(TP_DATA); //  Release the Data line so it goes high as the stop bit
+  delayMicroseconds(80); // testing shows delay at least 40us 
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  delayMicroseconds(1); // wait to let the data settle
+  if (digitalRead(TP_DATA)) { // Ack bit s/b low if good transfer
+  }
+  while ((digitalRead(TP_CLK) == LOW) || (digitalRead(TP_DATA) == LOW)) { // loop if clock or data are low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+// Inhibit the bus so the tp only talks when we're listening
+  go_0(TP_CLK);
+}
+//
+// Function to get a byte of data from the touchpad
+//
+char tp_read(void)
+{
+  unsigned int timeout = 200; // breakout of loop if over this value in msec
+  elapsedMillis watchdog; // zero the watchdog timer clock
+  char rcv_data = 0; // initialize to zero
+  char mask = 1; // shift a 1 across the 8 bits to select where to load the data
+  char rcv_parity = 0; // count the ones received
+  go_pu(TP_CLK); // release the clock
+  go_pu(TP_DATA); // release the data
+  delayMicroseconds(5); // delay to let clock go high
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    } 
+  }
+  if (digitalRead(TP_DATA)) { // Start bit s/b low from tp
+  // start bit not correct - put error handler here if desired
+  }  
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  for (int k=0; k<8; k++) {  
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+      if (watchdog >= timeout) { //check for infinite loop
+        init_error = HIGH;
+        break; // break out of infinite loop
+      }
+    }
+    if (digitalRead(TP_DATA)) { // check if data is high
+      rcv_data = rcv_data | mask; // set the appropriate bit in the rcv data
+      rcv_parity++; // increment the parity bit counter
+    }
+    mask = mask << 1;
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+      if (watchdog >= timeout) { //check for infinite loop
+        init_error = HIGH;
+        break; // break out of infinite loop
+      }
+    }
+  }
+// receive parity
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  if (digitalRead(TP_DATA))  { // check if received parity is high
+    rcv_parity++; // increment the parity bit counter
+  }
+  rcv_parity = rcv_parity & 1; // mask off all bits except the lsb
+  if (rcv_parity == 0) { // check for bad (even) parity
+    init_error = HIGH;
+  } 
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+// stop bit
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+  if (digitalRead(TP_DATA) == LOW) { // check if stop bit is bad (low)
+  // send bad stop bit to future error handler
+  }
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    if (watchdog >= timeout) { //check for infinite loop
+      init_error = HIGH;
+      break; // break out of infinite loop
+    }
+  }
+// Inhibit the bus so the tp only talks when we're listening
+  go_0(TP_CLK);
+  return rcv_data; // pass the received data back
+}
+//
+// Function to decode 3 bytes of data from the touchpad = status, X Delta, Y Delta
+//
+void tp_packet(void)           
+{
+// ******************************Receive Byte 0 = Status***********************
+  char rcv_data = 0; // initialize to zero
+  char mask = 1; // shift a 1 across the 8 bits to select where to load the data
+  char rcv_parity = 0; // count the ones received
+  go_pu(TP_CLK); // release the clock
+  go_pu(TP_DATA); // release the data
+  delayMicroseconds(5); // delay to let clock go high
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA)) { // Start bit s/b low from tp
+  // start bit not correct - put error handler here if desired
+  }  
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  for (int k=0; k<8; k++) {  
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    }
+    if (digitalRead(TP_DATA)) { // check if data is high
+      rcv_data = rcv_data | mask; // set the appropriate bit in the rcv data
+      rcv_parity++; // increment the parity bit counter
+    }
+    mask = mask << 1;
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    }
+  }
+// receive parity
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA))  { // check if received parity is high
+    rcv_parity++; // increment the parity bit counter
+  }
+  rcv_parity = rcv_parity & 1; // mask off all bits except the lsb
+  if (rcv_parity == 0) { // check for bad (even) parity
+    bit_error = HIGH;
+  } 
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+// stop bit
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA) == LOW) { // check if stop bit is bad (low)
+    bit_error = HIGH;
+  }
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  mstat = rcv_data; // save data result in status byte
+// ******************************Receive Byte 1 = Delta X**************************  
+  rcv_data = 0; // initialize to zero
+  mask = 1; // shift a 1 across the 8 bits to select where to load the data
+  rcv_parity = 0; // count the ones received
+  delayMicroseconds(5); // delay to let the clock stop ringing
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA)) { // Start bit s/b low from tp
+  // start bit not correct - put error handler here if desired
+  }  
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  for (int k=0; k<8; k++) {  
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    }
+    if (digitalRead(TP_DATA)) { // check if data is high
+      rcv_data = rcv_data | mask; // set the appropriate bit in the rcv data
+      rcv_parity++; // increment the parity bit counter
+    }
+    mask = mask << 1;
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    }
+  }
+// receive parity
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA))  { // check if received parity is high
+    rcv_parity++; // increment the parity bit counter
+  }
+  rcv_parity = rcv_parity & 1; // mask off all bits except the lsb
+  if (rcv_parity == 0) { // check for bad (even) parity
+    bit_error = HIGH;
+  } 
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+// stop bit
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA) == LOW) { // check if stop bit is bad (low)
+    bit_error = HIGH;
+  }
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  mx = rcv_data; // save data result in delta x byte
+// Receive Byte 1 = Delta Y  
+// ******************************Receive Byte 2 = Delta Y**************************  
+  rcv_data = 0; // initialize to zero
+  mask = 1; // shift a 1 across the 8 bits to select where to load the data
+  rcv_parity = 0; // count the ones received
+  delayMicroseconds(5); // delay to let the clock stop ringing
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA)) { // Start bit s/b low from tp
+  // start bit not correct - put error handler here if desired
+  }  
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  for (int k=0; k<8; k++) {  
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+    }
+    if (digitalRead(TP_DATA)) { // check if data is high
+      rcv_data = rcv_data | mask; // set the appropriate bit in the rcv data
+      rcv_parity++; // increment the parity bit counter
+    }
+    mask = mask << 1;
+    delayMicroseconds(1); // delay to let the clock settle out
+    while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+    }
+  }
+// receive parity
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA))  { // check if received parity is high
+    rcv_parity++; // increment the parity bit counter
+  }
+  rcv_parity = rcv_parity & 1; // mask off all bits except the lsb
+  if (rcv_parity == 0) { // check for bad (even) parity
+    bit_error = HIGH;
+  } 
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+// stop bit
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == HIGH) { // loop until the clock goes low
+  }
+  if (digitalRead(TP_DATA) == LOW) { // check if stop bit is bad (low)
+    bit_error = HIGH;
+  }
+  delayMicroseconds(1); // delay to let the clock settle out
+  while (digitalRead(TP_CLK) == LOW) { // loop until the clock goes high
+  }
+  my = rcv_data; // save data result in delta y byte
+//
+// Inhibit the bus so the tp only talks when we're listening
+  go_0(TP_CLK);
+}
+//
+void touchpad_init()
+{
+  init_error = LOW; // start with no error
+  go_pu(TP_CLK); // float the clock and data to touchpad
+  go_pu(TP_DATA);
+  //  Sending reset command to touchpad
+  tp_write(0xff);
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+  delay(1000); // wait 1 second so tp can run its self diagnostic
+  //  verify proper response from tp
+  if (tp_read() != 0xaa) { // verify basic assurance test passed
+    init_error = HIGH;
+  } 
+  if (tp_read() != 0x00) { // verify basic assurance test passed
+    init_error = HIGH;
+  }
+  //  Send touchpad disable code so that the mode byte can be loaded next
+  tp_write(0xf5);  // tp disable 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+  // Load Mode Byte with 00 using the following special sequence from page 38 of Synaptics Interfaceing Guide.
+  // Send set resolution to 0 four times followed by a set sample rate to 0x14
+  // The resolution and sample rate are not actually changed but instead it loads the mode byte.
+// #1 set resolution
+  tp_write(0xe8);  // set resolution (actually part of setting mode byte)
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  tp_write(0x00);  // to zero 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+// #2 set resolution (actually part of setting mode byte)
+  tp_write(0xe8);  // set resolution 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  tp_write(0x00);  // to zero 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+// #3 set resolution
+  tp_write(0xe8);  // set resolution 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  tp_write(0x00);  // to zero 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+// #4 set resolution (actually part of setting mode byte)
+  tp_write(0xe8);  // set resolution 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  tp_write(0x00);  // to zero 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+// Set sample rate (actually part of setting mode byte)
+  tp_write(0xf3);  // set sample rate 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  tp_write(0x14);  // to 14 hex 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  } 
+// This completes the mode byte load
+  // set the resolution for real
+  tp_write(0xe8); //  Sending resolution command
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  } 
+  tp_write(0x03); // value of 0x03 = 8 counts/mm resolution (default is 4 counts/mm)
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  } 
+  // set the sample rate for real
+  tp_write(0xf3); //  Sending sample rate command
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  } 
+  tp_write(0x28); // 0x28 = 40 samples per second, the default value used for Synaptics TP
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }  
+  //  Load stream mode command so tp will send data whenever it's available
+  tp_write(0xea);  // stream mode 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  } 
+  //  Send touchpad enable code 
+  tp_write(0xf4);  // tp enable 
+  if (tp_read() != 0xfa) { // verify correct ack byte
+    init_error = HIGH;
+  }
+}
+//
+// ************************************Begin Routine*********************************************************
+void setup() {
+  pinMode(ERROR_LED, OUTPUT); // define teensy I/O 13 as an output
+  touchpad_init(); // reset tp and check that self diagnostic passed. Put tp in stream mode and enable it 
+  digitalWrite(ERROR_LED, init_error); //LED off means touchpad passed its power up test, ACKed all communications, and never caused a watchdog timeout
+  delay(5000);  // wait 5 seconds to show init_error LED status
+  digitalWrite(ERROR_LED, LOW); // Turn off LED for 1/2 second 
+  delay(500);  // 1/2 second delay
+  digitalWrite(ERROR_LED, HIGH); // Turn on LED momentarily to indicate code is in main loop 
+  delay(500); // 1/2 second delay
+  digitalWrite(ERROR_LED, bit_error); // Turn off LED and switch its function to show bit errors in main loop
+}
+//
+// declare and initialize variables  
+  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() {
+// Touchpad is enabled and in stream mode
+  tp_packet(); // this function loops until there is bus activity and then saves data into mstat, mx, and my bytes for USB transmission below.
+  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 by throwing away lsb
+  mx = mx & 0x7f; // mask off 8th bit
+  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 by throwing away lsb 
+  my = my & 0x7f; // mask off 8th bit
+  if ((0x20 & mstat) == 0x20) {   // move the sign into 
+    my = 0x80 | my;              // the 8th bit position
+  } 
+// Invert the 8 bit value because y movement in ps/2 format is the opposite direction in touchpad.move function
+  my = (~my + 0x01); // invert the y data by taking the 2's complement (invert and add 1)
+// zero out mx and my if over_flow is detected because the data is garbage
+  if (over_flow) { 
+    mx = 0x00;       
+    my = 0x00;
+    bit_error = HIGH; // flag an error
+  } 
+// Send the x and y data back via usb if either one is non-zero
+  if ((mx != 0x00) || (my != 0x00)) {
+    Mouse.move(mx,my);
+  }
+//
+// pull out the left and right button status bits from the mstat byte 
+  if ((0x01 & mstat) == 0x01) {   // is bit 1 set 
+    left_button = 1;   // set the left_button status
+  }
+  else {   // clear the left_button status
+    left_button = 0;   
+  }
+  if ((0x02 & mstat) == 0x02) {   // is bit 2 set 
+    right_button = 1;   // set the right_button status
+  } 
+  else {   // clear the right_button status
+    right_button = 0;  
+  }
+// Determine if the left or right touch pad buttons have changed
+  button_change = (left_button ^ old_left_button) | (right_button ^ old_right_button);
+// Don't send button status if there's no change since last usb button transmission. 
+  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;
+  }
+//
+  digitalWrite(ERROR_LED, bit_error); // LED is used to show NACK, bad parity, overflow, or bad stop bits. Any error is latched "on"
+}