Arduino Uno post.

1 files changed, 38 insertions, 37 deletions

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@@ -67,52 +67,53 @@ oscillator.</p>
 
 <h2 id="5v-16mhz-configuration">5V-16MHz configuration</h2>
 
-<ol>
-  <li>Connect pin 1 to 5V via a 10kΩ resistor.</li>
-  <li>Connect a 16MHz crystal oscillator across pins 9 and 10.</li>
-  <li>Connect each pin of the crystal to ground via 22pF capacitors.</li>
-  <li>Connect pins 7, 20, and 21 to 5V.</li>
-  <li>Connect pins 8 and 22 to ground.</li>
-</ol>
-
-<p>In addition to the the connections above, it’s a good idea to add 0.1μF
-decoupling capacitors between pins 7, 20, and 21 and ground.
-<a href="Makefile">Here’s</a> a sample Makefile for avr-gcc and avrdude.</p>
+<p>Powering ATmega328P microcontrollers with 5V is the most common setup. This is
+also how Arduino Uno boards are wired.</p>
+
+<p>In this configuration, the microcontroller’s pin 1 is connected to 5V via a
+10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via
+two 22pF capacitors connected to ground. The microcontroller is powered by
+connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22
+are connected to ground. In addition to the these connections, which are
+required, it’s a good idea to add 0.1μF decoupling capacitors between pins 7,
+20, and 21 and ground.</p>
+
+<p><a href="Makefile">Here’s</a> a sample Makefile for compiling C programs for ATmega328P
+microcontrollers using avr-gcc/avrdude toolchain.</p>
 
 <h2 id="33v-8mhz-configuration">3.3V-8MHz configuration</h2>
 
-<p>Standard ATmega328P chips are preconfigured to run at 5V. To run one at 3.3V,
-we must first modify its fuses (e.g., BOD level). If the chip contains a
-pre-installed bootloader that expects a 16MHz clock (such as the Arduino Uno
-bootloader), it must be replaced with one that is more amenable to an 8MHz
-clock.</p>
-
-<p>In the following steps, we use an Arduino Uno as an in-system programmer to
-replace the embedded bootloader and modify the appropriate fuses.</p>
-
-<ol>
-  <li>Upload the ‘ArduinoISP’ sketch to the Arduino Uno.</li>
-  <li>Wire up the ATmega328P IC as described in the previous section, while
-replacing the 5V supply with a 3.3V supply and 16MHz crystal with an 8MHz
-crystal.</li>
-  <li>Connect the SPI ports (SCK, MISO, and MOSI) of the two MCUs.</li>
-  <li>Connect the Arduino Uno’s SS pin to the IC’s RESET pin (pin 1).</li>
-  <li>Connect the IC’s V<sub>CC</sub> to a 5V supply (e.g., the Arduino Uno’s 5V
-pin).</li>
-  <li>Burn the bootloader to the ATmega328P:
-    <ul>
-      <li>Select ‘ATmega328P (3.3V, 8MHz)’ from Tools &gt; Processor.</li>
-      <li>Select ‘Arduino as ISP’ from Tools &gt; Programmer.</li>
-      <li>Select Tools &gt; Burn Bootloader.</li>
-    </ul>
-  </li>
-</ol>
+<p>Electrical connections for running an ATmega328P at 3.3V are identical to that
+of the 5V circuit. The only differences are that all the 5V connections are
+replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place
+of the 16MHz crystal.</p>
+
+<p>However, standard ATmega328P chips are preconfigured to run at 5V. To run one
+at 3.3V, we must first modify its fuses that control characteristics like the
+BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino
+bootloader) is pre-installed on the ATmega328P, it must be swapped with one
+that accepts an 8MHz clock. To accomplish that, we need an in-system programmer
+(ISP).</p>
+
+<p>Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading
+the ‘ArduinoISP’ sketch found in the Arduino IDE. The ISP communicates with the
+microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI
+port of the ATmega328P to that of the Arduino Uno, and the Uno’s SS pin
+to the ATmega328P’s RESET pin.</p>
+
+<p>Power up the the ATmega328P by connecting its V<sub>CC</sub> to a 5V supply (we
+can use Arduino Uno’s 5V pin). From the Arduino IDE, select ‘ATmega328P (3.3V,
+8MHz)’ for processor from the tools menu. Also from the tools menu, select
+‘Arduino as ISP’ as programmer. Finally, upload the new bootloader by selecting
+‘Burn Bootloader’ from the tools menu.</p>
 
 <p>The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can
 upload programs to the ATmega328P as you normally would using avrdude.
 <a href="3v3.Makefile">Here’s</a> a sample Makefile with adjusted parameters (e.g., baud
 rate) for an 8MHz clock.</p>
 
+<h2 id="remarks">Remarks</h2>
+
 <p>In both configurations, if you intend to use the ATmega328P’s analog-to-digital
 converter with the internal 1.1V or AV<sub>cc</sub> voltage as reference, do
 not connect AREF (pin 21) to V<sub>cc</sub>. Refer to section 23.5.2 in the