W79E648 Datasheet, PDF (9/80 Pages) Winbond – Fast 8051 Compatible microcontroller with a redesigned Processor

Preliminary W79E648
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 W79E648 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
APROM0
64K Bytes
On-chip
Program
Memory
APROM1
0000h
4K Bytes
LDROM
0FFFh
Figure 1. Memory Map
Publication Release Date: 05/31/2004
-9-
Revision A1