W77LE58 datasheet(7/82 Pages) ETC2

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W77LE58/W77L058A

Publication Release Date: April 17, 20067

- 7 -

Revision A7

6. MEMORY ORGANIZATION

The W77L058 separates the memory into two separate sections, the Program Memory and the Data

Memory. The Program Memory is used to store the instruction op-codes, while the Data Memory is used

to store data or for memory mapped devices.

Program Memory

The Program Memory on the W77L058 can be up to 64 Kbytes long. There is also on-chip ROM which

can be used similarly to that of the 8052, except that the ROM size is 32 Kbytes. All instructions are

fetched for execution from this memory area. The MOVC instruction can also access this memory

region. Exceeding the maximum address of on-chip ROM will access the external memory.

Data Memory

The W77L058 can access up to 64Kbytes of external Data Memory. This memory region is accessed by

the MOVX instructions. Unlike the 8051 derivatives, the W77L058 contains on-chip 1K bytes MOVX

SRAM of Data Memory, which can only be accessed by MOVX instructions. These 1K bytes of SRAM

are between address 0000H and 03FFH. Access to the on-chip MOVX SRAM is optional under software

control. When enabled by software, any MOVX instruction that uses this area will go to the on-chip RAM.

MOVX addresses greater than 03FFH automatically go to external memory through Port 0 and 2. When

disabled, the 1KB memory area is transparent to the system memory map. Any MOVX directed to the

space between 0000H and FFFFH goes to the expanded bus on Port 0 and 2. This is the default

condition. In addition, the W77L058 has the standard 256 bytes of on-chip Scratchpad RAM. This can be

accessed either by direct addressing or by indirect addressing. There are also some Special Function

Registers (SFRs), which can only be accessed by direct addressing. Since the Scratchpad RAM is only

256 bytes, it can be used only when data contents are small. In the event that larger data contents are

present, two selections can be used. One is on-chip MOVX SRAM , the other is the external Data

Memory. The on-chip MOVX SRAM can only be accessed by a MOVX instruction, the same as that for

external Data Memory. However, the on-chip RAM has the fastest access times.

0000h

FFFFh

80h

7Fh

00h

64 K

Bytes

External

Data

Memory

Indirect

Addressing

RAM

Direct &

Indirect

Addressing

RAM

SFRs

Direct

Addressing

FFh

FFFFh

0000h

External

Program

Memory

7FFFh

32K Bytes

On-chip

Program

Memory

1K Bytes

On-chip SRAM

0000h

03FFh

Figure 1. Memory Map

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