W79E225A_08 Datasheet, PDF (13/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A Data Sheet
6. MEMORY ORGANIZATION
The W79E22X SERIES separates the memory into two sections; Program Memory and Data Memory.
Program Memory stores instruction op-codes, while Data Memory stores data or memory-mapped
devices.
6.1 Program Memory (on-chip Flash)
W79E22X SERIES includes one 16/32/64K bytes of main FLASH EPROM for application program (AP
FLASH EPROM) and one 4K bytes of FLASH EPROM for loader program (LD FLASH EPROM) to
operate the in-system programming (ISP) feature, and one 1/2/2K bytes of NVM Flash EPROM for
data storage. The 16/32/64K bytes Flash EPROM is AP0 bank. The default active bank is AP0.
In normal operation, the microcontroller will execute the code from main FLASH EPROM. By setting
program registers, user can force the microcontroller to switch to programming mode which will cause
it to execute the code (loader program) from the 4K bytes of auxiliary LD FLASH EPROM to update
the contents of the 16/32/64K bytes of main FLASH EPROM. After reset, the microcontroller will
executes the new application program in the main FLASH EPROM. This ISP feature makes the job
easy and efficient in which the application needs to update firmware frequently without opening the
chassis.
6.2 Data Memory
W79E22X SERIES can access up to 64Kbytes of external Data Memory. This memory region is
accessed by the MOVX instructions. Unlike the 8051 derivatives, W79E22X SERIES contains on-chip
1/2/2 Kbytes of Data Memory, which only can be accessed by MOVX instructions. These 1/2/2 Kbytes
of SRAM is between address 0000h and 03FFH/07FFH. Access to the on-chip Data Memory is
optional under software control. When enabled by DMEO bit of PMR register, a MOVX instruction that
uses this area will go to the on-chip RAM. If MOVX instruction accesses the addresses greater than
03FFH/07FFH CPU will automatically access external memory through Port 0 and 2. When disabled,
the 1/2/2 KB 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 the Port 0 and 2. This is the default
condition. In addition, the device has the standard 256 bytes of on-chip 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.
- 13 -
Publication Release Date: April 15, 2008
Revision A4.0