W77C32 Datasheet, PDF (8/78 Pages) Winbond – 8 BIT MICROCONTROLLER

W77C32/W77C032A
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.
FFh
80h
7Fh
00h
Indirect
Addressing
RAM
Direct &
Indirect
Addressing
RAM
SFRs
Direct
Addressing
only
FFFFh
64 K
Bytes
External
Data
Memory
FFFFh
64K bytes
of
External
Program
Memory
03FFh
0000h
1K Bytes
On-chip SRAM
0000h
Figure 1. Memory Map
0000h
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