Z51F0410 Datasheet, PDF (46/184 Pages) Zilog, Inc. – Z8051 Series 8-Bit Microcontrollers

Z51F0410
Product Specification
FFh
Upper
128 Bytes
Internal RAM
(Indirect
80h
Addressing)
7Fh
Lower
128 Bytes
Internal RAM
(Direct or Indirect
Addressing)
00h
FFh
Special Function
Registers
128 Bytes
(Direct Addressing)
80h
The internal memory space is divide^Fd^igi^un^rt^eo ²th^.2re^De^atb^alo^mc^ek^ms,^ow^ryh^mich^apare generally referred to as the lower
128, upper 128, and SFR space.
Internal Data memory addresses are always one byte wide, which implies an address space of only
256 bytes. However, the addressing modes for internal RAM can in fact accommodate 384 bytes,
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 2.2 shows the upper 128
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 2.3. 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 used 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 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 user RAM
and stack pointer.
PS029502-0212
PRELIMINARY
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