Banks; Direct Page - Renesas 7700 FAMILY User Manual

CENTRAL PROCESSING UNIT (CPU)
2.3 Access space

2.3.1 Banks

The access space is divided in units of 64 Kbytes. This unit is called "bank." The high-order 8 bits of
address (24 bits) indicate a bank, which is specified by the program bank register (PG) or data bank
register (DT). Each bank can be accessed efficiently by using an addressing mode that uses the data bank
register (DT).
If the program counter (PC) overflows at a bank boundary, the contents of the program bank register (PG)
is incremented by 1. If a borrow occurs in the program counter (PC) as a result of subtraction, the contents
of the program bank register (PG) is decremented by 1. Normally, accordingly, the user can program
without concern for bank boundaries.
SFR (Special Function Register), internal RAM, and internal ROM are assigned in bank 0
refer to section "2.4 Memory assignment."

2.3.2 Direct page

A 256-byte space specified by the direct page register (DPR) is called "direct page." A direct page is
specified by setting the base address (the lowest address) of the area to be specified as a direct page into
the direct page register (DPR).
By using a direct page addressing mode, a direct page can be accessed with less instruction cycles than
otherwise.
Note: Refer also to section "2.1 Central processing unit."
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