Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
CPU
(3) Frame base register (FB)
Frame base register (FB) is configured with 16 bits, and is used for FB relative addressing.
(4) Program counter (PC)
Program counter (PC) is configured with 20 bits, indicating the address of an instruction to be executed.
(5) Interrupt table register (INTB)
Interrupt table register (INTB) is configured with 20 bits, indicating the start address of an interrupt vector
table.
(6) Stack pointer (USP/ISP)
Stack pointer comes in two types: user stack pointer (USP) and interrupt stack pointer (ISP), each config-
ured with 16 bits.
Your desired type of stack pointer (USP or ISP) can be selected by a stack pointer select flag (U flag).
This flag is located at the position of bit 7 in the flag register (FLG).
(7) Static base register (SB)
Static base register (SB) is configured with 16 bits, and is used for SB relative addressing.
(8) Flag register (FLG)
Flag register (FLG) is configured with 11 bits, each bit is used as a flag. Figure 1.5.2 shows the flag
register (FLG). The following explains the function of each flag:
• Bit 0: Carry flag (C flag)
This flag retains a carry, borrow, or shift-out bit that has occurred in the arithmetic/logic unit.
• Bit 1: Debug flag (D flag)
This flag enables a single-step interrupt.
When this flag is “1”, a single-step interrupt is generated after instruction execution. This flag is
cleared to “0” when the interrupt is acknowledged.
• Bit 2: Zero flag (Z flag)
This flag is set to “1” when an arithmetic operation resulted in 0; otherwise, cleared to “0”.
• Bit 3: Sign flag (S flag)
This flag is set to “1” when an arithmetic operation resulted in a negative value; otherwise, cleared to “0”
.
• Bit 4: Register bank select flag (B flag)
This flag chooses a register bank. Register bank 0 is selected when this flag is “0” ; register bank 1 is
selected when this flag is “1”.
• Bit 5: Overflow flag (O flag)
This flag is set to “1” when an arithmetic operation resulted in overflow; otherwise, cleared to “0”.
• Bit 6: Interrupt enable flag (I flag)
This flag enables a maskable interrupt.
An interrupt is disabled when this flag is “0”, and is enabled when this flag is “1”. This flag is cleared to
“0” when the interrupt is acknowledged.
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MITSUBISHI [ Mitsubishi Group ]
