Rainbow Electronics AT89C5131 - Manual (Page 61)

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AT89C5131
4136A–USB–03/03
On-chip Expanded
RAM (XRAM)
The AT89C5131 provides additional Bytes of random access memory (RAM) space for
increased data parameter handling and high level language usage.
AT89C5131 devices have expanded RAM in external data space; maximum size and
location are described in Table 48.
The AT89C5131 has on-chip data memory that is mapped into the following four sepa-
rate 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 48)
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
Table 48. Description of Expanded RAM
Part Number XRAM Size
Address
Start End
AT89C5131 1024 00h 3FFh
XRAM
Upper
128 bytes
Internal
RAM
Lower
128 bytes
Internal
RAM
Special
Function
Register
80h 80h
00
0FFh or 3FFh 0FFh
00
0FFh
External
Data
Memory
0000
00FFh up to 03FFh
0FFFFh
indirect accesses
direct accesses
direct or indirect
accesses
7Fh