HD404669 Datasheet, PDF (17/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 Series
Data Area ($090–$2EF): 464 digits from $090 to $25F have two banks, which can be selected by setting
the bank register (V: $03F). Before accessing this area, set the bank register to the required value (figure
7). The area from $026 to $2EF is accessed without setting the bank register.
Bank register (V: $03F)
Bit
Initial value
Read/Write
Bit name
3
2
1
0
—
—
—
0
—
—
—
R/W
Not used Not used Not used V0
V0
Bank area selection
0
Bank 0 is selected
1
Bank 1 is selected
Note: After reset, the value in the bank register is 0, and therefore bank 0 is
selected.
Figure 7 Bank Register (V)
Stack Area ($3C0–$3FF): Used for saving the contents of the program counter (PC), status flag (ST), and
carry flag (CA) at subroutine call (CAL or CALL instruction) and for interrupts. This area can be used as a
16-level nesting subroutine stack in which one level requires four digits. The data to be saved and the save
conditions are shown in figure 6.
The program counter is restored by either the RTN or RTNI instruction, but the status and carry flags can
only be restored by the RTNI instruction. Any unused space in this area is used for data storage.
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