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CHAPTER 3 CPU ARCHITECTURE
Preliminary User’s Manual U16035EJ1V0UM
(a) Interrupt enable flag (IE)
This flag controls the interrupt request acknowledge operations of the CPU.
When 0, the IE is set to the disable interrupt (DI) state, and only non-maskable interrupt request becomes
acknowledgeable. Other interrupt requests are all disabled.
When 1, the IE is set to the enable interrupt (EI) state and interrupt request acknowledge enable is controlled
with an in-service priority flag (ISP), an interrupt mask flag for various interrupt sources and a priority
specification flag.
The IE is reset (0) upon DI instruction execution or interrupt acknowledgement and is set (1) upon EI
instruction execution.
(b) Zero flag (Z)
When the operation result is zero, this flag is set (1). It is reset (0) in all other cases.
(c) Register bank select flags (RBS0 and RBS1)
These are 2-bit flags to select one of the four register banks.
In these flags, the 2-bit information which indicates the register bank selected by SEL RBn instruction
execution is stored.
(d) Auxiliary carry flag (AC)
If the operation result has a carry from bit 3 or a borrow at bit 3, this flag is set (1). It is reset (0) in all other
cases.
(e) In-service priority flag (ISP)
This flag manages the priority of acknowledgeable maskable vectored interrupts. When this flag is 0, low-
level vectored interrupt requests specified with a priority specification flag register (PR0L, PR0H, PR1L) (refer
to
15.3 (3) Priority specification flag registers (PR0L, PR0H, PR1L)
) are disabled for acknowledgement.
When it is 1, all interrupts are acknowledgeable. Actual request acknowledgement is controlled with the
interrupt enable flag (IE).
(f)
Carry flag (CY)
This flag stores overflow and underflow upon add/subtract instruction execution. It stores the shift-out value
upon rotate instruction execution and functions as a bit accumulator during bit manipulation instruction
execution.
(3) Stack pointer (SP)
This is a 16-bit register to hold the start address of the memory stack area. Only the internal high-speed RAM
area can be set as the stack area. The internal high-speed RAM areas of each product are as follows.
Table 3-4. Internal High-Speed RAM Area
Part Number
Internal High-Speed RAM Area
µ
PD780021AS, 780022AS, 780031AS, 780032AS
FD00H to FEFFH
µ
PD780023AS, 780024AS, 780033AS, 780034AS,
FB00H to FEFFH
78F0034BS
