UPD75518 NEC, UPD75518 Datasheet - Page 38

• Manufacturer Part Number: UPD75518
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

38
3.8 BANK SELECT REGISTER (BS)
(MBS), which specify a register bank and memory bank to be used, respectively.
BS/POP BS instruction.
(1) Memory bank select register (MBS)
(2) Register bank select register (RBS)
The bank select register consists of a register bank select register (RBS) and memory bank select register
The RBS and MBS are set using the SEL RBn instruction and SEL MBn instruction, respectively.
The contents of BS can be saved to or restored from a stack area eight bits at a time by using the PUSH
The memory bank select register is a 4-bit register used to store the high-order four bits of a 12-bit data
memory address. The contents of this register specify a memory bank to be accessed. Note, however,
that the PD75518(A) allows only memory banks 0, 1, 2, 3, and 15 to be specified.
The MBS is set with the SEL MBn instruction (n = 0, 1, 2, 3, 15)
Fig. 2-1 shows the range of addressing using MBE and MBS settings.
A RESET signal occurrence initializes the MBS to 0.
The register bank select register specifies a register bank to be used as general registers; a register bank
can be selected from register banks 0 to 3.
The RBS is set with the SEL RBn instruction (n = 0 to 3).
A RESET signal occurrence initializes the RBS to 0.
Remark
: Don’t care
Address
Table 3-5 Register Bank to Be Selected with the RBE and RBS
RBE
0
1
MBS3 MBS2 MBS1 MBS0
3
0
0
Fig. 3-11 Bank Select Register Format
2
0
0
F83H
MBS
RBS
Always 0
1
0
0
1
1
0
0
1
0
1
Bank 0 is always selected.
Bank 0 is selected.
Bank 1 is selected.
Bank 2 is selected.
Bank 3 is selected.
0
0
F82H
RBS
Register bank
RBS1
RBS0
Symbol
BS
PD75518(A)