AT89LP6440 datasheet(12/194 Pages) ATMEL

12 / 194 page

3706A–MICRO–9/09

AT89LP6440 - Preliminary

3.2.2

IDATA

The full 256 byte internal RAM can be indirectly addressed using the 8-bit pointers R0 and R1.

The first 128 bytes of IDATA include the DATA space. The hardware stack is also located in the

IDATA space when XSTK = 0.

3.2.3

SFR

The upper 128 direct addresses (80H–FFH) access the I/O registers. I/O registers on AT89LP

devices are referred to as Special Function Registers. The SFRs can only be accessed through

direct addressing. All SFR locations are not implemented. See Section 4. for a listed of available

SFRs.

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 3-3. These memory spaces may require configuration before

the CPU can access them. The AT89LP6440 includes 4K bytes of on-chip Extra RAM (EDATA)

and 8K bytes of nonvolatile Flash data memory (FDATA).

Figure 3-3.

External Data Memory Map

3.3.1

XDATA

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

AT89LP6440 uses the standard 8051 external 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. MOVX instructions targeted to XDATA require a minimum of 4 clock cycles. XDATA can

be accessed with both 16-bit (MOVX @DPTR) and 8-bit (MOVX @Ri) addresses. See Section

3.3.4 on page 16 for more details of the external memory interface.

Extra RAM

(EDATA: 4KB)

0FFF

2FFF

3000

Flash Data

(FDATA: 8KB)

0000

0FFF

1000

FFFF

External Data

(XDATA: 64KB)

External Data

(XDATA: 60KB)

Extra RAM

(EDATA: 4KB)

External Data

(XDATA: 52KB)

FFFF

1000

EXRAM = 1

EXRAM = 0

DMEN = 0

EXRAM = 0

DMEN = 1

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