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Chapter 2 CPU Basics
Overview
Address Registers (A0, A1)
These registers are used as address pointers specifying data locations in memory. They support the
operations involved in address calculations (i.e. addition, subtraction and comparison). Those pointers
are 2 bytes data. Transfers between these registers and memory are always in 16-bit units. Either odd or
even address can be transferred. At reset, the value of address register is undefined.
Stack Pointer (SP)
This register gives the address of the byte at the top of the stack. It is decremented during push opera-
tions and incremented during pop operations. Ar reset, the value of SP is undefined.
2-1-6 Registers for Data
Registers for data include four data registers (D0, D1, D2, D3).
Data Registers (D0, D1, D2, D3)
Data registers D0 to D3 are 8-bit general-purpose registers that support all arithmetic, logical and shift
operations. All registers can be used for data transfers with memory.
The four data registers may be paired to form the 16-bit data registers DW0 (D0+D1) and DW1 (D2+D3).
At reset, the value of Dn is undefined.
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Address Registers
A0
A1
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Stack Pointer
SP
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DW0
DW1
D0
D2
D1
D3
Data
registers