DS89C430 Maxim, DS89C430 Datasheet - Page 19

• Manufacturer Part Number: DS89C430
• Description: The DS89C430 and DS89C450 offer the highest performance available in 8051-compatible microcontrollers
• Manufacturer: Maxim

Table 2. SFR Reset Value (continued)
Note: Consult the Ultra-High-Speed Flash Microcontroller User’s Guide for more information about the bits marked “Special.”
Memory Organization
There are three distinct memory areas in the DS89C430: scratchpad registers, program memory, and data
memory. The registers are located on-chip but the program and data memory spaces can be on-chip, off-chip, or
both. The DS89C430/DS89C450 have 16kB/64kB of on-chip program memory, respectively, implemented in flash
memory and also have 1kB of on-chip data memory space that can be configured as program space using the
PRAME bit in the ROMSIZE feature. The DS89C430 uses a memory-addressing scheme that separates program
memory from data memory. The program and data segments can be overlapped since they are accessed in
different manners. If the maximum address of on-chip program or data memory is exceeded, the DS89C430
performs an external memory access using the expanded memory bus. The PSEN signal goes active low to serve
as a chip enable or output enable when performing a code fetch from external program memory. MOVX
instructions activate the RD or WR signal for external MOVX data memory access. The program memory
ROMSIZE feature allows software to dynamically configure the maximum address of on-chip program memory.
This allows the DS89C430 to act as a bootloader for an external memory. It also enables the use of the
overlapping external program spaces. The lower 128 bytes of on-chip flash memory—if ROMSIZE is greater than
0—are used to store reset and interrupt vectors. 256 bytes of on-chip RAM serve as a register area and program
stack, which are separated from the data memory.
Register Space
Registers are located in the 256 bytes of on-chip RAM labeled “internal registers”
into two sub areas of 128 bytes each. Separate classes of instructions are used to access the registers and the
program/data memory. The upper 128 bytes are overlapped with the 128 bytes of SFRs in the memory map.
Indirect addressing is used to access the upper 128 bytes of scratchpad RAM, while the SFR area is accessed
using direct addressing. The lower 128 bytes can be accessed using direct or indirect addressing.
There are four banks of eight working registers in the lower 128 bytes of scratchpad RAM. The working registers
are general-purpose RAM locations that can be addressed within the selected bank by any instructions that use
R0–R7. The register bank selection is controlled through the program status register in the SFR area. The contents
of the working registers can be used for indirect addressing of the upper 128 bytes of scratchpad RAM.
Individually addressable bits in the RAM and SFR areas support Boolean operations. In the scratchpad RAM area,
registers 20h–2Fh are bit addressable by software using Boolean operation instructions.
Another use of the scratchpad RAM area is for the stack. The stack pointer, contained in the SFRs, is used to
select storage locations for program variables and for return addresses of control operations.
REGISTER
WDCON
FDATA
FCNTL
PSW
ACC
EIP1
EIP0
TH2
TL2
EIE
B
ADDRESS
CCh
CDh
D0h
D5h
D6h
D8h
E0h
E8h
F1h
F8h
F0h
BIT 7
0
0
0
1
0
0
0
1
0
1
1
Special
BIT 6
0
0
0
0
0
0
1
0
1
1
DS89C430/DS89C450 Ultra-High-Speed Flash Microcontrollers
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BIT 5
0
0
0
1
0
0
0
1
0
1
1
Special
BIT 4
0
0
0
0
0
0
0
1
0
0
BIT 3
0
0
0
0
0
0
0
0
0
0
0
(Figure
Special
BIT 2
0
0
0
0
0
0
0
0
0
0
6), which can be divided
Special
BIT 1
0
0
0
0
0
0
0
0
0
0
BIT 0
0
0
0
0
0
0
0
0
0
0
0