UPD78320 Datasheet, PDF (22/88 Pages) NEC – 16/8-BIT SINGLE-CHIP MICROCONTROLLER

µPD78320, 78322
(f) Auxiliary carry flag (AC)
If a carry is generated out of bit 3 as a result of operation or a borrow is generated into bit 3, this flag is set to 1. In
all other cases, this flag is reset to 0. This flag can be tested by the conditional branch instruction.
(g) Register set select flag (RSS)
This flag is used to specify general registers which function as X, A, C and B. As shown in Table 2-1, the RSS value
determines the relationship between the functional register and the absolute register.
Thus, another register set (X, A, C, B) can be used by switching the RSS flag.
(h) Interrupt request enable flag (IE)
This flag is used to indicate interrupt request enable/disable. This flag is set to 1 by execution of EI instruction and
is reset to 0 by execution of DI instruction or acceptance of an interrupt.
(i) Register bank select flag (RBS0 to RBS2)
This is a 3-bit flag to select one of eight register banks (RBANK0 to RBANK7).
(j) User flag (UF)
This flag is set or reset in the user program and can be used for program control.
(3) Stack pointer (SP)
This is a 16-bit register which holds the first address of the stack area (LIFO format) of the memory. It is manipulated
by a dedicated instruction.
SP is decremented before write (save) operation into the stack memory and is incremented after read (restore)
operation from the stack memory.
Since SP becomes indeterminate by RESET input, it must be set before subroutine call, etc..
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