AT89LP51RB2 datasheet(17/254 Pages) ATMEL

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3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

3.3

External Data Memory

AT89LP microcontrollers support a 16-bit external memory address space for up to 64K bytes of

external data memory (XDATA). The external memory space is accessed with the MOVX

instructions. Some internal data memory resources are mapped into portions of the external

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

the CPU can access them. The AT89LP51RB2/RC2/IC2 includes 1152 bytes of on-chip Extra

RAM (EDATA).

3.3.1

XDATA

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

AT89LP51RB2/RC2/IC2 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 3.3.2 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.

Addr es se s a bove t h e r a ng e imple m ent ed int e rn a lly will def au l t t o X D AT A. The

AT89LP51RB2/RC2/IC2 supports up to 60–62K bytes of external memory when using the inter-

nally mapped memories. Setting the EXTRAM bit (AUXR.1) to one will force all MOVX

instructions to access the entire 64KB XDATA regardless of their address (See “AUXR – Auxil-

iary Control Register” on page 19).

Figure 3-6.

External Data Memory Map

Extra RAM

(EDATA: 1KB)

03FF

Flash Program

(CODE: 32KB)

0000

0400

FFFF

External Data

(XDATA: 64KB)

External Data

(XDATA: 62KB)

FFFF

7FFF

EXRAM = 1

XRS = x

FPS = x

EXRAM = 0

XRS = 011B

FPS = 0

EXRAM = 0

XRS = x

FPS = 1

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