W79E632A Datasheet, PDF (7/79 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E632A/W79L632A
6. MEMORY ORGANIZATION
The W79E(L)632 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. By invoking the
banking methodology, W79E(L)632 can extend to two 64KB flash EPROM banks, APFlash0 and
APFlash1. There are on-chip ROM banks which can be used similarly to that of the 8052. 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). Both APFlashs allow serial or parallel download according to user loader
program in LDFlash.
Data Memory
The W79E(L)632 can access up to 64Kbytes of external Data Memory. This memory region is accessed
by the MOVX instructions. Unlike the 8051 derivatives, the W79E(L)632 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 W79E(L)632 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.
Publication Release Date: Nov. 11, 2009
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Revision A10