3. PROGRAM MEMORY - ROM ROM ( READ ONLYMEMORY ) 8051 can address 4K bytes on chip memory – map range 0000 TO 0FFFh IT can address 64 KB external memory map range – 0000 TO FFFFh Memory map of internal and external program overlaps The internal and external ROM distinguished by PSEN’ signal ROM less version of 8051 – PSEN’ used to access external memory
5. DATA MEMORY - RAM EXTERNAL RAM 8051 supports 64KB external data memory- range – 0000 to FFFFh Accessed by DPTR 8051 generates RD’, WR’ during external access . CS’ can be derived from address lines
9. Registers 1F 18 Bank 3 Four Register Banks Each bank has R0-R7 Selectable by psw.2,3 17 10 Bank 2 0F 08 Bank 1 07 06 05 04 03 02 01 00 R7 R6 R5 R4 R3 R2 R1 R0 Bank 0
10. Bit Addressable Memory 2F 2E 2D 2C 2B 2A 29 28 20h – 2Fh (16 locations X 8-bits = 128 bits) Bit addressing: mov C, 1Ah or mov C, 23h.2 27 26 25 24 23 22 21 20
20. I/O INTERFACING External i/o devices are interfaced as memorymapped i/o devices Devicestreated as externalmemory locations and consume externalmemoryaddress The address of external program and data memorymayoverlap
