NEC PD754144 - Manual (Page 77)

CHAPTER 4 INTERNAL CPU FUNCTION
77 User’s Manual U10676EJ3V0UM
(5) Register bank enable flag (RBE)
This flag specifies whether the register bank of the general-purpose registers is expanded or not.
RBE can be set or reset at any time by using a bit manipulation instruction, regardless of the setting of the
memory bank.
When this flag is set to “1”, one of four general-purpose register banks 0 to 3 can be selected depending on
the contents of the register bank select register (RBS).
When RBE is reset to “0”, register bank 0 is always selected, regardless of the contents of the register bank
select register (RBS).
When the RESET signal is asserted, the contents of bit 6 of program memory address 0 are set to RBE, and
RBE is automatically initialized.
When a vector interrupt occurs, the contents of bit 6 of the corresponding vector address table are set to RBE.
Also, the status of RBE when the interrupt is serviced is automatically set. Usually, RBE is reset to 0 during
interrupt servicing. Register bank 0 is selected for 4-bit processing, and register banks 0 and 1 are selected
for 8-bit processing.