UPD784938 Datasheet, PDF (85/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 3 CPU ARCHITECTURE
(4) Auxiliary carry flag (AC)
The AC flag is set (to 1) when there is a carry out of bit 3 or a borrow into bit 3 as the result of an operation, and reset (to
0) otherwise.
This flag is used when the ADJBA or ADJBS instruction is executed.
(5) Register set selection flag (RSS)
The RSS flag specifies the general-purpose registers that function as X, A, C, and B, and the general-purpose register pairs
(16-bit) that function as AX and BC.
This flag is provided to maintain compatibility with the 78K/III Series, and must be set to 0 except when using a 78K/III Series
program.
(6) Zero flag (Z)
The Z flag records the fact that the result of an operation is “0”.
It is set (to 1) when the result of an operation is “0”, and reset (to 0) otherwise. The status of the Z flag can be tested with
a conditional branch instruction.
(7) Sign flag (S)
The S flag records the fact that the MSB is “1” as the result of an operation.
It is set (to 1) when the MSB is “1” as the result of an operation, and reset (to 0) otherwise. The status of the S flag can be
tested with a conditional branch instruction.
(8) Register bank selection flag (RBS0 to RBS2)
This is a 3-bit flag used to select one of the 8 register banks (register bank 0 to register bank 7) (see Table 3-4).
It stores 3-bit information which indicates the register bank selected by execution of a SEL RBn instruction, etc.
Table 3-4. Register Bank Selection
RBS2
0
0
0
0
1
1
1
1
RBS1
0
0
1
1
0
0
1
1
RBS0
0
1
0
1
0
1
0
1
Specified Register Bank
Register bank 0
Register bank 1
Register bank 2
Register bank 3
Register bank 4
Register bank 5
Register bank 6
Register bank 7
(9) User flag (UF)
This flag can be set and reset in the user program, and used for program control.
Preliminary User’s Manual U13987EJ1V0UM00
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