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CHAPTER 3 CPU ARCHITECTURE
User’s Manual U12697EJ3V0UM
(5) Register set selection flag (RSS)
This flag sets the general-purpose registers that function as X, A, C, and B and the general-purpose register pairs
(16 bits) that function as AX and BC.
This flag is used to maintain compatibility with the 78K/III Series. Always set this flag to 0 except when using
a 78K/III Series program.
(6) Zero flag (Z)
This flag indicates that the operation result is 0.
If the operation result is 0, this flag is set to 1. Otherwise, it is reset to 0. The state of the Z flag can be tested
by conditional branch instructions.
(7) Sign flag (S)
This flag indicates that the MSB in the operation result is 1.
The flag is set to 1 when the MSB of the operation result is 1. If 0, the flag is reset to 0. The S flag state can
be tested by the conditional branch instructions.
(8) Register bank selection flags (RBS0 to RBS2)
This is the 3-bit flag that selects one of the eight register banks (register banks 0 to 7). (refer to
Table 3-4
.)
Three bit information that indicates the register bank selected by executing the SEL RBn instruction is stored.
Table 3-4. Register Bank Selection
RBS2
RBS1
RBS0
Set Register Bank
0
0
0
Register bank 0
0
0
1
Register bank 1
0
1
0
Register bank 2
0
1
1
Register bank 3
1
0
0
Register bank 4
1
0
1
Register bank 5
1
1
0
Register bank 6
1
1
1
Register bank 7
(9) User flag (UF)
This flag is set and reset by a user program and can be used in program control.
