Datasheet

78K0/Kx2-L CHAPTER 3 CPU ARCHITECTURE
R01UH0028EJ0400 Rev.4.00 77
Sep 27, 2010
(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 that 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 by a priority specification flag register (PR0L, PR0H, PR1L, PR1H) (refer to
17.3 (3) Priority specification flag registers (PR0L, PR0H, PR1L, PR1H)) can not be acknowledged. Actual
request acknowledgment is controlled by 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 operation 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.
Figure 3-11. Format of Stack Pointer
15
SP
SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
0
The SP is decremented ahead of write (save) to the stack memory and is incremented after read (restored) from the
stack memory.
Each stack operation saves/restores data as shown in Figures 3-12 and 3-13.
Caution Since reset signal generation makes the SP contents undefined, be sure to initialize the SP before
using the stack.