UPD78323LP datasheet(21/86 Pages) NEC

21 / 86 page

µPD78323, 78324

(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 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 byexecution of DI instruction or acceptance of an interrupt.

(i)

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 operated by a dedicated instruction.

SP is decremented before write (save) operation into the stack memory and is incremented after read (return) operation

from the stack memory.

Since SP becomes indeterminate by RESET input, it must be set before subroutine call.

UPD78323LP 데이터시트(PDF) 21 Page - NEC