Editing Electrical Onboarding/PSoC getting started (Blink) (section)

=Exercise 1=
Try adding four LEDs to a breadboard circuit with 1K ohm resistors in series. Connect the anode of each LED to a PSoC pin as shown in the schematic below. Write some code to create a binary counter that will count up every one second, and reset to 0 once a value of 0x10 (16 in decimal) is reached. In the PSoC Creator schematic, call each of your pins '''LED0, LED1, LED2,''' and '''LED3''' in order to match the solution code.

{{Screenshot|Image:led_counter.png| Binary LED counter schematic using PSoC5}}

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<div style="font-weight:bold;line-height:1.6;">Solution</div>
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<pre>
#include "project.h"

int main(void)
{
    int count = 0;
    char pin_val[4];

    CyGlobalIntEnable; /* Enable global interrupts. */

    /* Place your initialization/startup code here (e.g. MyInst_Start()) */

    for(;;)
    {
        pinval[0] = count&1;
        pinval[1] = (count&2)>>1;
        pinval[2] = (count&4)>>2;
        pinval[3] = (count&8)>>3;

        LED0_Write(pinval[0]);
        LED1_Write(pinval[1]);
        LED2_Write(pinval[2]);
        LED3_Write(pinval[3]);

        count++;
        count = count%0x10;

        CyDelay(1000);
    }
}
<pre>
This code works by incrementing a counter variable every second. The counter variable is used to determine the pin state of each LED. For LED0, since it is representing the least significant bit (LSB) of the binary number it will be bit-wise ANDed with the LSB of count (i.e. '''pinval[0] = count&1'''). This will give a value of 1 when the LSB is a 1, and 0 when the LSB is a 0. 

We repeat this logic for the other pins as well, but need to do a bitwise shift. If we just did '''pinval[1] = count&2''' then when the second bit of the count variable is a 1, '''pinval[1] = 2''' which is not a valid argument for the '''Write()''' macro that only accepts a value of 1 or 0. The extra bitwise shift effectively divides by 2 for every shift done, so 2/2 = 1 which is valid. This logic is used for the other two pins as well.
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