AT89LP51 datasheet(14/113 Pages) ATMEL

14 / 113 page

3709B–MICRO–12/10

AT89LP51/52 - Preliminary

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 19).

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

not accessible while DMEN = 0. FDATA can be accessed only by 16-bit (MOVX @DPTR)

addresses. MOVX @Ri instructions to the FDATA address range will access external memory.

Addresses above the FDATA range are mapped to XDATA.

3.3.2.1

Write Protocol

The FDATA address space accesses an internal nonvolatile data memory. This address space

can be read just like EDATA by issuing a MOVX A,@DPTR; however, writes to FDATA require a

more complex protocol and take several milliseconds to complete.

For internal execution the AT89LP51/52 uses an idle-while-write architecture where the CPU is

placed in an idle state while the write occurs. When the write completes, the CPU will continue

executing with the instruction after the MOVX @DPTR,A instruction that started the write. All

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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