7220 Datasheet, PDF (29/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

FUNCTIONAL DESCRIPTION
2.1 Central processing unit
2.1 Central processing unit
The CPU of the M37221M6-XXXSP/FP has six main registers.
The program counter (PC) is a 16-bit register consists of PCH and PCL, both of which are 8-bit registers.
The other five registers: the accumulator (A), index register X (X), index register Y (Y), stack pointer (S) and
processor status register (PS), all have an 8-bit configuration.
Note: The contents of registers above except the following are indeterminate after a hardware reset. Therefore,
initialize these registers by software.
• The Interrupt disable flag I of the processor status register = “1”
• The program counter = the contents of addresses FFFE16 and FFFF16
Figure 2.1.1 shows the registers configuration diagram of M37221M6-XXXSP/FP.
7
0
A
Accumulator (A)
7
0
X
Index Register X (X)
7
0
Y
Index Register Y (Y)
7
0
S
Stack Pointer (S)
7
07
0
PCH
PCL
Program Counter (PC)
7
0
N V T B D I Z C Processor Status Register (PS)
Fig. 2.1.1 Registers configuration diagram
Carry Flag
Zero Flag
Interrupt Disable Flag
Decimal Operation Mode Flag
Break Flag
X Modified Operation Mode Flag
Overflow Flag
Negative Flag
2.1.1 Accumulator (A)
The accumulator is the central register of the microcomputer and 8-bit register.
This general-purpose register is used with considerable for arithmetic operations, data transfer, temporary
clearing, condition judgments, etc.
2.1.2 Index register X (X), index register Y (Y)
The M37221M6-XXXSP/FP has the index register X and the index register Y, both of which are 8-bit
registers.
In the addressing modes which use these index registers, the register contents are added to the specified
address and this becomes the actual address. These modes are used for referencing subroutine tables and
memory tables.
The index registers, which have increment, decrement, comparison and data transfer functions, are also
used as simple accumulators.
2-2
7220 Group User’s Manual