Parallax Propeller Book - Programming Part 2

Reading Inputs

Prerequisites:

Equipment:

Components:

Objective:

Reading Switches

Reading Pull UP Switch

Project #4.2-1

Reading Input, controlling Output

To read the Input of P10 we will use the circuit in Figure 3-10.

Switch with Down Up Resistor
Fig 3-10 Switch with Pull Down Resistor

To control the Output on P26 we will use the circuit in Figure 3-7a or in Figure 3-7b.

Port Output HI
Fig 3-7a LED Status Indicator for Port Output HI
Port Output HI
Fig 3-7b LED Status Indicator for Port Output HI

The ina register is a Read-Only register in Cog RAM whose bits store the voltage state of each I/O pin.

When an I/O pin is set to output, its ina register bit will report the same value as the outa register bit since ina bits indicate high/low I/O pin voltages with 1 and 0.

If the I/O pin is instead an input, its ina register bit updates based on the voltage applied to it.

If a voltage above the I/O pin’s 1.65 V logic threshold is applied, the ina register bit stores a 1; otherwise, it stores a 0.

The ina register is updated with the voltage states of the I/O pins each time an ina command is issued to read this register.

The push-button connected to P10 will apply 3.3 V to P10 when pressed, or 0 V when not pressed.

In the ButtonToLed object below, dira[10] is set to 0, making I/O pin P10 function as an input.

So, it will store 1 if the P10 push-button is pressed, or 0 if it is not pressed.

By repeatedly assigning the value stored in ina[10] to outa[26], the ButtonLed method makes the P26 LED light whenever the P10 push-button is pressed.

Notice also that the command outa[26] := ina[10] is indented below the repeat command, which causes this line to get executed over and over again indefinitely.

4.2-1_ButtonP10ToLedP26.spin

Click the link above to download the Spin Code listed below in .txt format

'' 4.2-1_ButtonP10ToLedP26.spin
'' LED mirrors push-button state.
'' Project #4.2-1 Reading Input, controlling Output

PUB ButtonLed 			'Push-button/Led Method
	
dira[26] := 1 		' P26 → output
dira[10] := 0 		' P10 → input (this command is redundant)
	
repeat 			' endlessly loop code below
	outa[26] := ina[10] 	
                ' Copy P10 input (push-button) to P26 output (LED)

Reading Pull DOWN Switch

Project #4.2-2

Reading Input, controlling Output

To read the Input of P11 we will use the circuit in Figure 3-11.

Switch with Down Up Resistor
Fig 3-11 Switch with Pull Up Resistor

To control the Output on P26 we will use the circuit in Figure 3-7a or in Figure 3-7b.

Port Output HI
Fig 3-7a LED Status Indicator for Port Output HI
Port Output HI
Fig 3-7b LED Status Indicator for Port Output HI

The ina register is a Read-Only register in Cog RAM whose bits store the voltage state of each I/O pin.

When an I/O pin is set to output, its ina register bit will report the same value as the outa register bit since ina bits indicate high/low I/O pin voltages with 1 and 0.

If the I/O pin is instead an input, its ina register bit updates based on the voltage applied to it.

If a voltage above the I/O pin’s 1.65 V logic threshold is applied, the ina register bit stores a 1; otherwise, it stores a 0.

The ina register is updated with the voltage states of the I/O pins each time an ina command is issued to read this register.

The push-button connected to P11 will apply 0 V to P11 when pressed, or 3.3 V when not pressed.

In the ButtonToLed object below, dira[11] is set to 0, making I/O pin P11 function as an input. So, it will store 0 if the P11 push-button is pressed, or 1 if it is not pressed.

By repeatedly assigning the value stored in ina[11] to outa[26], the ButtonLed method makes the P26 LED light whenever the P11 push-button is NOT pressed.

Notice also that the command outa[26] := ina[11] is indented below the repeat command, which causes this line to get executed over and over again indefinitely.

4.2-2_ButtonP11ToLedP26.spin

Click the link above to download the Spin Code listed below in .txt format

'' 4.2-2_ButtonP11ToLedP26.spin
'' Led mirrors pushbutton state.
'' Project #4.2-2 Reading Input, controlling Output

PUB ButtonLed 			'Pushbutton/Led Method
	
dira[26] := 1 		' P26 → output
dira[11] := 0 		' P11 → input (this command is redundant)
	
repeat 				' Endlessly loop code below
	outa[26] := ina[11] 	' Copy P11 input to P26 output

Spinning Spin

Another way to copy input to output.

Using The Bitwise NOT - “!”

• Replace this:

outa[26] := ina[11]

• ... with this:

outa[26] := !ina[11]

This will reverse the button functionality to LED ON when button is pressed.

Reading Signals

Reading Ground Signal

Project #4.2-3

Reading Input, controlling Output

To read the Input on P15 we will use the circuit in Figure 3-11.
Note: The "SW" can be any device that provides Ground Signal to the P15 port.

Switch with Down Up Resistor
Fig 3-11 Switch with Pull Up Resistor

To control the Output on P27 we will use the circuit in Figure 3-7a or in Figure 3-7b.

Port Output HI
Fig 3-7a LED Status Indicator for Port Output HI
Port Output HI
Fig 3-7b LED Status Indicator for Port Output HI

The ina register is a Read-Only register in Cog RAM whose bits store the voltage state of each I/O pin.

When an I/O pin is set to output, its ina register bit will report the same value as the outa register bit since ina bits indicate high/low I/O pin voltages with 1 and 0.

If the I/O pin is instead an input, its ina register bit updates based on the voltage applied to it.

If a voltage above the I/O pin’s 1.65 V logic threshold is applied, the ina register bit stores a 1; otherwise, it stores a 0.

The ina register is updated with the voltage states of the I/O pins each time an ina command is issued to read this register. The signal applied to P15 will apply 0 V to P15 when "ON" , or 3.3 V when "OFF".

In the singleshot object below, dira[15] is set to 0, making I/O pin P15 function as an input. So, it will store 0 if the P15 Ground signal is present, or 1 if it is not present, that is P15 is HI.

The singleshot method makes the P27 LED light for specified time interval (1/2 second) whenever the P15 Ground signal is present for any duration.

Notice also that the command repeat while ina[15] == 0 is indented below the if ina[15] == 0 command, which causes this line to get executed over and over again indefinitely if the Ground signal is still present.

This results in a "single shot" of the output per each Ground input signal, irrespective of the Ground signal duration.

4.2-3_GSignalP15ToLedP27Timed.spin

Click the link above to download the Spin Code listed below in .txt format

'' 4.2-3_GSignalP15ToLedP27Timed.spin

PUB singleshot

  dira[27] := 1                      'Sets P27 to output [LED]
  dira[15] := 0                      'sets P15 to input 
				' [external signal 0V=ON  3.3V=OFF]

  repeat              'Endless loop prevents program from ending 
    if ina[15] == 0        'If GND signal present continue code
      outa[27]~~                  'Set P27 HI = Turn LED ON 
      waitcnt(clkfreq/2 + cnt)'Wait for specified time(1/2 second)
      outa[27]~                   'Set P27 LO = Turn LED OFF
      if ina[15] == 0 
                    'If GND signal is still present continue code
        repeat while ina[15] == 0 
                    'Loop while GND signal is still present

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