AT89C5131-RDTIL datasheet(46/176 Pages) ATMEL

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AT89C5131

4136B–USB–09/03

On-chip Expanded

RAM (ERAM)

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 45.

The AT89C5131 has on-chip data memory that is mapped into the following four sepa-

rate segments.

The Lower 128 bytes of RAM (addresses 00h to 7Fh) are directly and indirectly

addressable.

The Upper 128 bytes of RAM (addresses 80h to FFh) are indirectly addressable

only.

The Special Function Registers, SFRs, (addresses 80h to FFh) are directly

addressable only.

The expanded RAM bytes are indirectly accessed by MOVX instructions, and

with the EXTRAM bit cleared in the AUXR register (see Table 45)

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 22. Internal and External Data Memory Address

Table 45. Description of Expanded RAM

Part Number

ERAM Size

Address

Start

End

AT89C5131

1024

00h

3FFh

ERAM

Upper

128 bytes

Internal

RAM

Lower

128 bytes

Internal

RAM

Special

Function

80h

0FFh or 3FFh

0FFh

External

Data

Memory

0000

00FFh up to 03FFh

0FFFFh

indirect accesses

direct accesses

direct or indirect

accesses

7Fh

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