I'm trying to figure out the flash memory map of ATmega328P:
Below is from the datasheet:
Program Memory Map for ATmega328P is given as 32KB: 32Kbytes = 32K * bytes
0x0000 means 16 bit wide (for each line of memory there is 2 bytes)
which is 16K * 16bit
What I understand from this, the flash memory is made up of 16K lines of 16 bit wide registers. So for an instruction on the flash memory the maximum address number is 16K.
Is this 16K 2^16 or 16000?
The last three X Y Z general purpose registers which are used for holding the addresses(pointers) are 16-bit which can store up to 2^16 = 65536 addresses.
So I would guess 16K means 65536 here?
But if it is, in the above figure it shows the last memory line as 0x3FFF which corresponds to 16383.
What am I knowing wrong here?
Best Answer
What you are knowing wrong are a couple of things.
Not all AVR devices have the same amount of actual available on-chip program memory. Some may have 8K bytes, 16K bytes, 32K bytes or even 64K bytes. Yours happens to have the advertised 32K bytes.
The X, Y and Z registers are 16-bits wide. These are generically designed to support a data memory map up to 64K bytes. Once again the size of available data memory can vary from device to device type so the whole 64K byte addressability may not be used on all devices.
The X, Y and Z registers are generically indicated right in the data sheet description to be used for accessing data memory. Data memory is not to be confused with program memory. The Z register can be used, in conjunction with certain specific opcodes, to access tables in the program memory (Z still 16-bits to support up to a generic 64K bytes even though the program memory available may be less).