w77e58 Winbond Electronics Corp America, w77e58 Datasheet - Page 9

• Manufacturer Part Number: w77e58
• Description: 8 Bit Microcontroller
• Manufacturer: Winbond Electronics Corp America

Data Memory:
The W77E58 can access up to 64Kbytes of external Data Memory. This memory region is accessed
by the MOVX instructions. Unlike the 8051 derivatives, the W77E58 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 W77E58 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
7Fh
80h
00h
Addressing
Addressing
Direct &
Indirect
Indirect
RAM
RAM
03FFh
0000h
Addressing
Direct
SFRs
On-chip SRAM
1K Bytes
Figure 1. Memory Map
- 9 -
FFFFh
0000h
External
Memory
Bytes
Data
64 K
Preliminary W77E58
Publication Release Date: March 1999
0000h
7FFFh
FFFFh
32K Bytes
Program
Memory
On-chip
Program
External
Memory
Revision A1