the internal RAM are divided to two type . first one is SFR from 80 to FF memory location. direct addressing method used here
second one is from 00 to 7F. here we use DIRECT and INDIRECT addressing methods.
DIRECT ADDRESSING: we can specify the location. eg: we can specify 00 or 7F, can specify any address through instruction.
SFR: in SFR we use only direct addressing.
RAM.
ATMEL AT89C51 have a special type RAM.this RAM divided to 3 area.they are
1. SCRATCH PAD OR GENERAL PURPOSE RAM
2.BIT ADDRESSABLE AREA.
3.REGISTER BANK.
BIT ADDRESSABLE AREA: we can access each bits.
DATA MEMORY:
include 128 bytes of internal RAm,128 bytes of SFR ( internal memory)and 64KB of external memory.(EA to VCC)
Ea bar pin connected to VCC and CPU generate read RD bar and write WR bar signal as needed during external RAM access.
lower 128 bytes of data memory are direct or indirect addressable.SFR are direct addressable only.SFR are situated from the address location 80H to FFH.
Labels: ATMEL 89C51
