Now besides just blinking the LED, it would be nice to provide some information directly to the user. You can do this by working with the Serial Port and the Serial Monitor.
We learned how to store constants in Flash to avoid unnecessarily cluttering SRAM and we learned how to read data from Flash.
Now we're ready to learn how to write to Flash using C functions from avrlibc. Figure 2 shows the message I got after I rebooted. Everything recovered okay and I fixed the code to be blast free. But you never know Writing To Flash Flash is easy to read, but hard to write.
We learned that SRAM is the most expensive and only used to store data that changes a lot when the CPU is running; that EEPROM is cheaper and is useful for storing byte-sized constants that change occassionally; and finally, that Flash is cheapest of all and is used to store the program code that rarely changes.
This reduces the circuitry necessary to program Flash, thus making it cheaper. Flash page size varies depending on the particular AVR device.
Flash is addressed by words, not bytes. One additional noteworthy feature of Flash versus the other memory is that Flash stores data as bit words, meaning that eight-bit byte data is stored in either the high or low part of a word. For me, this creates a conceptual problem because for the AVR — which is an eight-bit system — we think in terms of bytes.
So, why is the memory now considered in words? Well, that is because the Flash memory itself is a peripheral something outside the CPU that is erased and written to in pages with word-sized boundaries. I find this confusing and suggest that you just do what I do: Try to remember that when the CPU is reading Flash memory, it is doing it in bytes but that when we are talking about actually erasing or writing to the Flash memory, we are doing that in page-sized chunks that are defined in words.
Later when we look at boot section addresses, we might notice things like the ATmega boot section that begins at 0x7E00, and if we translate that into decimal we might wonder why the bootsection begins at when we are using a 64K bytes memory.
The answer is, of course, that we are actually using a 32K word memory and that the boot section is a word address that corresponds to a byte address of 0xFC00 It can sometimes be confusing whether you are talking about words or bytes in Flash memory, so pay attention.
How Flash is written. Even if all we wanted to do in Flash is change a single byte, we have to find what page it is in, copy that whole page of bytes words to SRAM, and then wait while the SRAM gets written to Flash.
Most microcontrollers only have the program written once and they run it to the end of time. We, of course, are learning about these things, so will write the program code many times to both learn new stuff and to correct the inevitable mistakes we make.
Would you change code while it is running? A computer loads a sequence of instructions from the program memory and performs operations based on that code. We assume there is some logic to the design of that sequence so that, for instance, if we add two numbers then the result is used for some later instruction in the sequence.
But what if we could change the program sequence while it is running? As we introduced in Workshop 22, bootloaders write code to program memory. A bootloader is a module of code that writes code while it is running. You see the potential problem here? The AVR has special features that make it easier to safely use bootloaders.
One of these is to divide the program memory into two sections: This allows us to designate a section of memory that will not allow the CPU to read the program memory while writing to program memory. These boundaries are set by fuses that tell the AVR to run code beginning at that indicated address when coming out of reset.
In our Flash writing example [see Figure 3], we will use the smallest section available that begins at address 0x7E00 [remember that Flash is measured in words]. This means we have words or 1, bytes to store in our bootloader.
We will learn how to use this to write data to Flash and next month we will apply what we learn to developing a bootloader. We can continue to execute code in the NRWW section while parts of that section are being written to.
This allows our application to continue to run critical code while the rest of the program is being updated.
This could corrupt that page of Flash and when the power is restored, the program may be corrupted. Avrlibc is included in your WinAVR installation. We use the following functions: This sits around blocking further action until the Flash has finished writing. It is odd in that it uses a byte address but writes a word, so you have to load the high and low bytes of the tempWord and then add two to the address to load the next word.Secret Arduino Voltmeter – Measure Battery Voltage - A little known feature of Arduinos and many other AVR chips is the ability to measure the internal .
The ATmegaP features 32 KBytes of Flash, 2 KBytes of RAM, and 1 KByte of EEPROM a nice improvement over Arduino’s original configuration with an ATmega8: (8 KBytes of flash, 1 KByte of RAM, and Bytes of EEPROM).
Reading and Writing to the EEPROM Sometimes it can be useful to store numbers, or other data, into the Arduino’s EEPROM to protect it against power-cycling. Using the included EEPROM library it’s actually pretty easy to write a number to EEPROM.
Reading and Writing an External I2C 24LC EEPROM March 4, Arduino Directions Topographic Map Andy benjaminpohle.com This code demonstrates how to read and write any data type, such as strings to an external I2C EEPROM. Back to topic, this time we will discuss about reading and writing of data to Arduino’s internal EEPROM.
If RAM is volatile (lost when the power supply is turned off), then EEPROM is the opposite, which is non-volatile.
ATmega microcontroller has 1 Kb of EEPROM (ATmega and ATMega8 have Byte). Jun 03, · The spec sheet on the 16F88 rates the EEPROM at 1,, write cycles, so I don't think writing every second will work long term.
You might consider powering the PIC from a super-capacitor (e.g., 1F or better), and have the PIC monitor the incoming power.