W77C32 datasheet(8/78 Pages) WINBOND

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W77C32/W77C032A

- 8 -

6. MEMORY ORGANIZATION

The W77C032 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.

6.1 Program Memory

The Program Memory on the W77C032 can be up to 64Kbytes long. All instructions are fetched for

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

6.2 Data Memory

The W77C032 can access up to 64Kbytes of external Data Memory. This memory region is accessed

by the MOVX instructions. Unlike the 8051 derivatives, the W77C032 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 W77C032 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

only

FFh

FFFFh

0000h

64K bytes

External

Program

Memory

1K Bytes

On-chip SRAM

0000h

03FFh

Figure 1. Memory Map

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