UPD17P136ACT datasheet(65/292 Pages) NEC

65 / 292 page

CHAPTER 7 SYSTEM REGISTER (SYSREG)

000

BANK

79H

Address

Name

Symbol

Bit

Data

Initial value when

reset

Bank register

(BANK)

7.4 BANK REGISTER (BANK)

7.4.1 Bank Register Configuration

Figure 7-7 shows the configuration of the bank register.

The bank register consists of four bits at address 79H (BANK) of the system register. However, since the three

high-order bits are always set to 0, only the least significant bit is actually used.

All bits are set to 0 at reset.

Figure 7-7. Bank Register Configuration

7.4.2 Functions of Bank Register

The bank register is used to switch between the banks in data memory. Table 7-1 shows how the banks in data

memory are specified by the value in the bank register.

Table 7-1. Specifying the Bank in Data Memory

Bank register

Bank in data

memory

0000

BANK0

0001

BANK1

Data memory is effectively divided into two banks by the bank register. When a data memory manipulation

instruction is executed, the data memory in the bank specified by the bank register is manipulated.

Therefore, if the current bank is BANK0, in order to manipulate data memory in BANK1 (port registers), the bank

The system register can be manipulated regardless of the state of the bank register.

For example, whether the instruction MOV 78H, #0 is executed for BANK0 or BANK1, the effect is the same; 0

is written to address 78H of the system register.

In addition, BANK becomes 0 after saved to the interrupt stack register.

UPD17P136ACT Datasheet(PDF) 65 Page - NEC