Abov MC96F8104M, Руководство пользователя

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MC96F8204 ABOV Semiconductor Co., Ltd.
8.2 Data Memory
FFH
80H
7FH
00H
FFH
80H
Upper 128bytes
Internal RAM
(Indirect Addressing)
Special Function Registers
128bytes
(Direct Addressing)
Lower 128bytes
Internal RAM
(Direct or Indirect
Addressing)
Figure 8.2 Data Memory Map
The internal data memory space is divided into three blocks, which are generally referred to as the lower 128 bytes,
upper 128 bytes, and SFR space.
Internal data memory addresses are always one byte wide, which implies an address space of only 256 bytes.
However, in fact the addressing modes for internal RAM can accommodate up to 384 bytes by using a simple trick.
Direct addresses higher than 7FH access one memory space and indirect addresses higher than 7FH access a
different memory space. Thus Figure 8-2 shows the upper 128 bytes and SFR space occupying the same block of
addresses, 80H through FFH, although they are physically separate entities.
The lower 128 bytes of RAM are present in all 8051 devices as mapped in Figure 8-3. The lowest 32 bytes are
grouped into 4 banks of 8 registers. Program instructions call out these registers as R0 through R7. Two bits in the
Program Status Word select which register bank is in use. This allows more efficient use of code space, since register
instructions are shorter than instructions that use direct addressing.
The next 16 bytes above the register banks form a block of bit-addressable memory space. The 8051 instruction set
includes a wide selection of single-bit instructions, and the 128 bits in this area can be directly addressed by these
instructions. The bit addresses in this area are 00H through 7FH.
All of the bytes in the lower 128 bytes can be accessed by either direct or indirect addressing. The upper 128 bytes
RAM can only be accessed by indirect addressing. These spaces are used for data RAM and stack.