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3-1
CHAPTER 3
ADDRESS SPACES
MCS
®
251 microcontrollers have three address spaces: a memory space, a special function reg-
ister (SFR) space, and a register file. This chapter describes these address spaces as they apply to
all MCS 251 microcontrollers and to the 8XC251Sx in particular. It also discusses the compati-
bility of the MCS 251 architecture and the MCS
®
51 architecture in terms of their address spaces.
3.1 ADDRESS SPACES FOR MCS
®
251 MICROCONTROLLERS
Figure 3-1 shows the memory space, the SFR space, and the register file for MCS 251 microcon-
trollers. (The address spaces are depicted as being eight bytes wide with addresses increasing
from left to right and from bottom to top.)
Figure 3-1. Address Spaces for MCS
®
251 Microcontrollers
A4100-01
FF:FFFFH
SFR Space
512 Bytes
Memory Address Space
16 Mbytes
00:0000H
0
Register File
64 Bytes
7
63
S:000H
S:1FFH
00:0007H
S:007H