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BK2535 datasheet

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0X00 R0

0X07 BANK0

Figure 7 Internal Ram Lower 128 Bytes

The lower 128 bytes of Internal Data Memory is organized in three distinct areas:

0x00-0x1F: The Register Banks are at the lowest 32 bytes of the internal data

memory. Only one Register Bank is used at a time when an instruction uses R0

to R7. 2 bits in Processor Status Word (PSW), called RS1 and RS0, control the

selection of the Register Bank. Bank 0 is selected upon reset. Indirect addressing

mode used R0 and R1 as index registers

0x20-0x2F: This memory space contains a general-purpose memory, which is bit

addressable as well as byte addressable. The bit address ranged from 0 to 0x7F.

When bit addressing is used in an instruction, the bit access in this region will

occur. In this memory range, when bit addressing is used, bit address 0x00 is the

bit 0 of address 0x20 while bit 7 of the byte 0x20 has bit address 0x07. Bit

address 0x7F is the bit 7 of address 0x2F. A bit access is different than a byte

access by the type of instruction used.

0x30-0x7F: A general-purpose byte-addressable memory is located above

address 0x30. It can be accessed both by direct or indirect addressing mode.

5.2.4.3. Internal Ram: Upper 128 Bytes

The usage of the addresses between 0x80 and 0xFF is up to the user. This

memory can be used for any purpose providing that indirect addressing mode is

used when accessing this memory space, otherwise the Special Function

5.2.4.4. The Stack and the stack pointer

The stack refers to an area of internal RAM that is used in conjunction with

certain instructions (PUSH, POP) to store and retrieve data quickly. The Stack

pointer register (SP, 0x81) is used to hold an internal RAM address that is called

the “top of the stack”. The data held in the SP register is the address in internal

RAM where the last byte of data was stored by a stack operation. The reset

value of Stack pointer register is 0X07 and which can be changed to any internal

RAM address by the programmer. Usually, the stack is located high in the RAM

to avoid conflict with the work register, bit and byte area in internal RAM.

5.2.4.5. Special Function Registers

The direct-access data memory locations from 0x80 to 0xFF constitute the

special function registers (SFRs). All the special function registers of the original

80C51 are present in the Flip8051. SFRs with addresses ending in 0x0 or 0x8

(e.g. P0, TCON, P1, SCON, IE, etc.) are bit-addressable as well as byte-

addressable. All other SFRs are byte-addressable only.

BK2535 Datasheet(PDF) 21 Page - Beken Corporation