Datasheet

44
A/T89C51AC2
4127H–8051–02/08
Operation Cross Memory Access
Space addressable in read and write are:
• RAM
• ERAM (Expanded RAM access by movx)
• XRAM (eXternal RAM)
• EEPROM DATA
• FM0 (user flash)
• Hardware byte
• XROW
• Boot Flash
• Flash Column latch
The table below provide the different kind of memory which can be accessed from differ-
ent code location.
Note: 1. RWW: Read While Write
Table 27. Cross Memory Access
Action RAM
XRAM
ERAM Boot FLASH FM0 E² Data
Hardware
Byte XROW
boot FLASH
Read OK OK OK OK -
Write - OK
(1)
OK
(1)
OK
(1)
OK
(1)
FM0
Read OK OK OK OK -
Write - OK (idle) OK
(1)
- OK
External
memory
EA = 0
or Code Roll
Over
Read - - OK - -
Write - - OK
(1)
- -