W77LE516 Datasheet, PDF (8/89 Pages) Winbond – 8-BIT MICROCONTROLLER

W77LE516/W77L516A
6. MEMORY ORGANIZATION
The W77L516A 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 standard 8052 can only be addressed to 64 Kbytes long. All instructions
are fetched for execution from this memory area. The MOVC instruction can also access this memory
region. There is an auxiliary 4KB Flash EPROM bank (LDFLASH) resided user loader program for In-
System Programming (ISP). APFLASH allows serial or parallel download according to user loader
program in LDFLASH.
Data Memory
The W77L516A can access up to 64Kbytes of external Data Memory. This memory region is
accessed by the MOVX instructions. Unlike the 8051 derivatives, the W77L516A 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 W77L516A 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.
FFh
Indirect
Addressing
RAM
80h
7Fh
Direct &
Indirect
Addressing
00h
RAM
SFRs
Direct
Addressing
03FFh
0000h
1K Bytes
On-chip SRAM
64 K
Bytes
External
Data
Memory
FFFFh
64K Bytes
On-chip
Program
Memory
APROM
0000h
4K Bytes
LDROM
0FFFh
Figure 1. Memory Map
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