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162 lines
7.6 KiB
Plaintext
162 lines
7.6 KiB
Plaintext
/**
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@defgroup boards_atmega328p Standalone ATmega328p
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@ingroup boards
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@brief Support for using the ATmega328p as standalone board
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## Overview
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The ATmega328p is most popular in the Arduino UNO. However, the 28 PDIP package
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of the ATmega328p can easily be used without any "board": Just place it on a
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bread board, and connect a TTL adapter and an ISP and you're ready to go.
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The ATmega328p has two internal oscillators, one clocked at 8MHz and one at
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128kHz. By default the fuses of the ATmega328p are configured that the internal
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8MHz oscillator can be used. This allows the ATmega328p to be operated without
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any external components at a supply voltage anywhere between 2.7V and 5.5V.
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\htmlonly<style>div.image img[src="https://github.com/maribu/images/raw/master/ATmega328p.jpg"]{width:600px;}</style>\endhtmlonly
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@image html "https://github.com/maribu/images/raw/master/ATmega328p.jpg" "ATmega328p DIP package on a breadboard"<br>
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### MCU
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| MCU | ATmega328p |
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|:------------- |:--------------------------------------------- |
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| Family | AVR/ATmega |
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| Vendor | Microchip (previously Atmel) |
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| RAM | 2KiB |
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| Flash | 32KiB |
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| EEPROM | 1KiB |
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| Frequency | 1MHz/8MHz (up to 20MHz with external clock) |
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| Timers | 3 (2x 8bit, 1x 16bit) |
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| ADCs | 6 analog input pins |
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| UARTs | 1 |
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| SPIs | 1 |
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| I2Cs | 1 (called TWI) |
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| Vcc | 2.7V - 5.5V (when clocked at 8MHz) |
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| Datasheet | [Official datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf) |
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### Pinout
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\htmlonly<style>div.image img[src="https://camo.githubusercontent.com/c55beef2f138da61fe671a1e4a307ff4ffbc318d/68747470733a2f2f692e696d6775722e636f6d2f715849456368542e6a7067"]{width:100%;}</style>\endhtmlonly
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@image html "https://camo.githubusercontent.com/c55beef2f138da61fe671a1e4a307ff4ffbc318d/68747470733a2f2f692e696d6775722e636f6d2f715849456368542e6a7067" "Pinout of the ATmega328p"<br>
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All credit for above pinout image goes to https://github.com/MCUdude/MiniCore#pinout
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### Clock Frequency
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The ATmega328p has two internal oscillators clocked at 8MHz and at 128kHz that
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allow it to be operated without any external clock source or crystal. By default
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the fuses are configured to use the internal 8MHz oscillator and a clock divider
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resulting in a clock speed of 1MHz. By clearing the `CKDIV8` fuse the clock
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divider can be disabled to operate the ATmega328p at 8MHz without an external
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clock source. This can be done like this:
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avrdude -c usbtiny -p m328p -B 32 -U lfuse:w:0xe2:m
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(Replace `usbtiny` with the ISP programmer you are using. The `-B 32` might
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be needed on some ISP programmers to communicate with slow ATmega MCUs. It will
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not be needed anymore after the clock device has been disabled.)
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This "board" is configured to use 8MHz as core clock, so that the ATmega328p
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runs at the highest frequency possible without external clock sources.
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By setting the environment variable `ATMEGA328P_CLOCK` to a custom frequency in
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Hz (e.g. `1000000` for 1MHz), this core clock can be changed easily. Refer to
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the datasheet on how to configure the ATmega328p to use an external crystal,
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an external clock source or the clock divider.
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### Relation Between Supply Voltage, Clock Frequency and Power Consumption
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A higher supply voltage results in a higher current drawn. Thus, lower power
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consumption can be achieved by using a lower supply voltage. However, higher
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clock frequencies require higher supply voltages for reliable operation.
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The lowest possible supply voltage at 8 MHz is 2.7V (with some safety margin),
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which results in an active supply current of less than 3 mA (about 8 mW power
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consumption) according to the datasheet. At 1 MHz core clock a supply voltage of
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1.8V is possible resulting in an active supply current of less than 0.3 mA
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(about 0.5 mW power consumption). For more details, refer to the official
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datasheet.
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## Flashing the Device
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In order to flash the ATmega328P without a bootloader, an ICSP programmer is
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needed. Connect the programmer as follows:
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| ISCP pin | ATmega328p pin |
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|:-------- |:-------------- |
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| MISO | 18/PB4/MISO |
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| VCC | 7/VCC |
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| SCK | 19/PB5/SCK |
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| MOSI | 17/PB3/MOSI |
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| RESET | 1/RESET |
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| Ground | 22/GND |
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The tool `avrdude` needs to be installed. When using the `usbtiny` (or one of
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the super cheap clones) running
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make BOARD=atmega328p flash
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will take care of everything. To use the programmer `<FOOBAR>` instead, run
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make BOARD=atmega328p PROGRAMMER=<FOOBAR> flash
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## Serial Terminal
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Connect a TTL adapter with pins 2/RXD and 3/TXD an run
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make BOARD=atmega328p term
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Please note that the supply voltage should be compatible with the logic level of
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the TTL adapter. Usually everything between 3.3 V and 5 V should work.
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## On-Chip Debugging (OCD)
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E.g. with the AVR Dragon and [AVaRICE](http://avarice.sourceforge.net/) you
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can debug the ATmega328P using the debugWIRE interface. Compared to the ATmega
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MCUs with JTAG interface the debug facilities are however significantly reduced:
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Only a single hardware breakpoint and no watchpoints are supported. The
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hardware breakpoint is used for single-stepping. If you set breakpoints, the
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AVR Dragon will transparently replace the instruction to break upon with a
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break instruction. Once the breakpoint is hit, the break instruction is
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overwritten with the original instruction. Thus, every breakpoint hit cause two
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flash cycles to be performed, which not only results in a slow debugging
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experience, but also causes significant wear.
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In order to enable debugWIRE run (replace `<PROGRAMMER>` with the programmer you
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use, e.g. with `dragon_isp` if you use the AVR Dragon):
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avrdude -c <PROGRAMMER> -p m328p -U hfuse:w:0x99:m
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You can disable it again via:
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avrdude -c <PROGRAMMER> -p m328p -U hfuse:w:0xd9:m
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@warning As the reset pin is repurposed for debugWIRE, a regular ISP will
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not be able to disable the debugWIRE interface anymore. The AVR
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Dragon can temporary disable the debugWIRE interface via a
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debugWIRE command and avrdude will do so when debugWIRE is used.
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So only enable debugWIRE if you have an AVR DRagon or other means
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to disable debugWIRE later on again.
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For debugging, the ATmega328P needs to be connected to the AVR Dragon in the
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very same way it needs to be connected for programming (see above). Once the
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MCU is connected and debugWIRE is enabled via the fuse settings, you can start
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debugging via:
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make debug
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If this fails after flashing the ATmega328P, it is like due to debugWIRE
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being temporary disabled by avrdude in order to use the ISP feature. Perform a
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cold boot and the ATmega328P will have debugWIRE enabled again.
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@note If you are using a different debugger than the AVR Dragon, you have
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to export the `AVR_DEBUGDEVICE` environment variable to the required
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flag to pass to AVaRICE, e.g. when using the Atmel-ICE you have to
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export `AVR_DEBUGDEVICE=--edbg`. If the debug device is not
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connected via USB, you also need to export `AVR_DEBUGINTERFACE` to
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the correct value.
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## Caution
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Don't expect having a working network stack due to very limited resources ;-)
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*/
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