AT89LP51 datasheet(15/113 Pages) ATMEL

15 / 113 page

3709C–MICRO–5/11

AT89LP51/52 - Preliminary

address space as shown in Figure 3-6. These memory spaces may require configuration before

the CPU can access them. The AT89LP51/52 includes 256 bytes of nonvolatile Flash data

memory (FDATA).

3.3.1

XDATA

The external data memory space can accommodate up to 64KB of external memory. The

AT89LP51/52 uses the standard 8051 external data memory interface with the upper address

byte on Port 2, the lower address byte and data in/out multiplexed on Port 0, and the ALE, RD

and WR strobes. XDATA can be accessed with both 16-bit (MOVX @DPTR) and 8-bit (MOVX

@Ri) addresses. See Section 3.3.3 on page 18 for more details of the external memory

interface.

Some internal data memory spaces are mapped into portions of the XDATA address space. In

this case the lower address ranges will access internal resources instead of external memory.

Addresses above the range implemented internally will default to XDATA. The AT89LP51/52

supports up to 63.75K or 56K bytes of external memory when using the internally mapped mem-

ories. Setting the EXRAM bit (AUXR.1) to one will force all MOVX instructions to access the

entire 64KB XDATA regardless of their address (See “AUXR – Auxiliary Control Register” on

page 20).

Figure 3-6.

External Data Memory Map

3.3.2

FDATA

The Flash Data Memory is a portion of the external memory space implemented as an internal

nonvolatile data memory. Flash Data Memory is enabled by setting the DMEN bit (MEMCON.3)

to one. When IAP = 0 and DMEN = 1, the Flash Data Memory is mapped into the FDATA space,

at the bottom of the external memory address space, from 0000H to 00FFH. (See Figure 3-6).

MOVX instructions to this address range will access the internal nonvolatile memory. FDATA is

Flash Data

(FDATA: 256)

00FF

1FFF

2000

Flash Program

(CODE: 8KB)

0000

0100

FFFF

External Data

(XDATA: 64KB)

External Data

(XDATA: 63.75KB)

External Data

(XDATA: 56KB)

FFFF

EXRAM = 1 or

DMEN = 0

IAP = 0

EXRAM = 0

DMEN = 1

IAP = 0

EXRAM = 0

DMEN = x

IAP = 1

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