AT89C5131A-L_14 Datasheet, PDF (47/186 Pages) ATMEL Corporation – Maximum Core Frequency 48 MHz in X1 Mode, 24 MHz in X2 Mode

AT89C5131A-L
On-chip Expanded
RAM (ERAM)
The AT89C5131A-L provides additional Bytes of random access memory (RAM) space
for increased data parameters handling and high level language usage.
AT89C5131A-L devices have an expanded RAM in the external data space; maximum
size and location are described in Table 44.
Table 44. Description of Expanded RAM
Address
Part Number
ERAM Size
Start
End
AT89C5131A-L
1024
00h
3FFh
The AT89C5131A-L has on-chip data memory which is mapped into the following four
separate segments.
1. The Lower 128 bytes of RAM (addresses 00h to 7Fh) are directly and indirectly
addressable.
2. The Upper 128 bytes of RAM (addresses 80h to FFh) are indirectly addressable
only.
3. The Special Function Registers, SFRs, (addresses 80h to FFh) are directly
addressable only.
4. The expanded RAM bytes are indirectly accessed by MOVX instructions, and
with the EXTRAM bit cleared in the AUXR register (see Table 44)
The lower 128 bytes can be accessed by either direct or indirect addressing. The Upper
128 bytes can be accessed by indirect addressing only. The Upper 128 bytes occupy
the same address space as the SFR. That means they have the same address, but are
physically separate from SFR space.
Figure 25. Internal and External Data Memory Address
0FFh or 3FFh(*)
0FFh
0FFh
0FFFFh
ERAM
Upper
128 bytes
Internal
RAM
indirect accesses
80h
7Fh
Special
Function
Register
direct accesses
80h
External
Data
Memory
Lower
128 bytes
Internal
RAM
direct or indirect
accesses
00FFh up to 03FFh (*)
00
00
0000
(*) Depends on XRS1..0
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4338F–USB–08/07