SM8521 Datasheet, PDF (10/56 Pages) Sharp Electrionic Components – 8-Bit Single-Chip Microcomputer

SM8521
Register Lineup
Fig. 1 shows the SM85CPU register lineup. The CPU
internal register consists of eight 8-bit general purpose
registers (R0-R7), four 16-bit general purpose registers
(RR8-RR14), a program counter (PC) and four other
control registers. (The R0-R7 can be also used as
four 16-bit general purpose registers (RR8-RR14).)
7
RR0
RR2
RR4
RR6
15
RR8
RR10
RR12
RR14
07
R0
R2
R4
R6
R8
R10
R12
R14
7
7
7
7
07
SPH
15
PC
0
R1
R3
R5
R7
0
R9
R11
R13
R15
0
PS0
0
PS1
0
SYS
0
SPL
0
Fig. 1 Register Lineup
GENERAL PURPOSE REGISTER
The eight 8-bit general purpose registers R0-R7 and
all eight 16-bit general purpose registers (RR0-
RR14) are available for use as accumulator, index
register and pointer registers. (The R0 and RR0
cannot be used as index register)
The other eight 8-bit registers R8-R15 cannot be used
as 8-bit general purpose register and as member of
the register file. (about register file, refer to "Address
Space.")
The feature of the SM85CPU architecture is that
general purpose registers are virtually allocated at
16-byte internal RAM. Actually, if the CPU accesses
general purpose registers, the designated RAM will
be accessed by the 5-bit register pointer (RP)^V.
When RP = 00000B, the registers occupy the first
16 bytes starting at 0000H. Incrementing the field,
RP = 00001B, shifts the mapping by eight bytes so
that the registers start at 0008H. As a result, the
general purpose registers can be switched in 8-byte
unit to any RAM location within 0000H-00FFH.
Although the general purpose registers are members
of the register file, which stores the data onto
actual RAM, is different from the other members
(control registers).
That is, general purpose registers can be referred as
registers, as register file (allocated at 0000H-000FH)
and as RAM accessing by all addressing modes.
∗ About register pointer (RP), refer to "Processor status 0
(PS0)".
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