I am new to bootloader.simply I want to read memory adress of RAM.(0x20000000 8 byte)But I am getting 0x1F Which means NACK.
Please have a look on AN2606 for each STM32 MCU implementation of Area you can read/write/erase. Generally speaking The first Bytes/Kbytes of the RAM is used by the boot loader firmware ( RW, stack etc). So we Nack any read/Write to that area. Here an example of STM32F1.
You can read upper part of RAM it will be acked.
Retrieving data ...