For flash, writing is usually done a block at a time also. This number is given in the datasheet as a minimum guaranteed value. For flash, I have seen numbers as low as The feature is usually used to updated code in the field. The trick is that you need to leave some code in the system while the main program is being updated, called the bootloader.
This scheme is used in the Arduino system to program the chip. The ATmega16 implements an Harvard architecture , i. Quoting the relevant paragraph from the Atmega16 datasheet page 8 :. In order to maximize performance and parallelism, the AVR uses a Harvard architecture — with separate memories and buses for program and data.
Instructions in the program memory are executed with a single level pipelining. While one instruction is being executed, the next instruc- tion is pre-fetched from the program memory. This concept enables instructions to be executed in every clock cycle. The program memory is In-System Reprogrammable Flash memory. Harvard architecture has the advantage of having no bus contention between instruction fetching cycles and data access cycles, since data and instructions don't share the same bus, like in your conventional PC architecture.
Therefore the flash memory is used as the program memory, whereas the data memory is split between SRAM for transient data, like function call stack and the heap - if you are programming in C, for example and the EEPROM for permanent storage. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. Asked 6 years, 8 months ago. Active 4 years, 9 months ago. Viewed 28k times. Or Is my inference as given above from the datasheet is wrong? Adam Lawrence Jasser Jasser 1 1 gold badge 3 3 silver badges 17 17 bronze badges. Add a comment. Active Oldest Votes. Am i right Sir. You will also need to use these registers to read out of the EEPROM, since it will not show up in the normal address map.
Are these statements meaningful? This is typically much higher sometimes an order of magnitude more than the number of times you can update the flash. Usually the first two instructions set PCLATH are used for correct program page and the third instructions that is GOTO is used for code executing in another branch of program memory, otherwise a littler useful code can be used at the start of program memory if the interrupts are used.
During the code executing when the interrupt is occurring then the next instruction address is fetched and saved in stack. The branch instructions first three bits indicates that this instruction can be modify the program counter.
If we talk about the CALL instructions this also indicate the return address and the remaining bits are loaded into 11 least significant bits LSB of program counter, these 11 bits for addressing allows up to 2K of address.
This defines the program memory page size and the devices which have up to 2K program memory, the 2 most significant bit MSB of program counter is maintain clear for keeping PCLATH clear.
This is also a common in all the microcontrollers. The data memory is divide into 4 banks and each banks having a length bytes. For access to each bank the bits PR1 and PR0 of status register needs to be accessed. The special function register controls the various aspects of microcontroller depend upon the process architecture of microcontroller.
It controls the following functions of controller such as input, output and peripheral control, Timer, program counter, stack pointer, stack limit, condition codes and processor status. The general purpose registers store the transient type data.
For example, when the program is interrupted in its state then that value of address register, instruction register or program counter is saved in general purpose register.
This is nonvolatile its data can be written in many times. Here we take a look on the microcontroller processor architecture.
It controls the structure and memory size ultimately it controls the operational speed of microcontroller. The microcontroller has two most common architectures first one is Von Neumann architecture and second one is Harvard architecture.
The microcontrollers which have Von Neumann architecture have only a single memory space. This single space stores both the data and program instructions. Due to this reason the several instructions must be occur from a single memory spaces that is called fetches.
The instructions which executes again and again required a several fetches to fit in a single memory space. In this condition first fetch retrieves the CPU instructions and the additional fetches retrieves the data, which is required for program instruction.
By doing this decreases the bandwidth of microcontroller, because the date fetches must be wait until the program fetches instructions has completed. This is called Von Neumann bottleneck. Shown in figure 3. PIC microcontroller units use the Harvard architecture because these microcontrollers have separate data and program memory.
Therefore, in pic microcontroller units the fetching of instructions and fetching of data executes simultaneously in a single fetching operation results increased throughput. This architecture also has another advantage that it program and data bus can be tailored with performance requirements. Its data bus is always being 8-bits wide but the microchip offers the microcontroller, which have , , bits program memory width. Increasing the width allows greater no of instructions to be fetch but still the fetching operation is in a single fetch operation.
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