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XC2200 Derivatives
System Units (Vol. 1 of 2)
Central Processing Unit (CPU)
User’s Manual
4-40
V2.1, 2008-08
CPUSV2_X, V2.2
Physical Address = Base A
∆
×
Short Address
Note:
∆
is 1 for byte GPRs,
∆
is 2 for word GPRs.
Rw, Rb:
Specifies direct access to any GPR in the currently active context (global
register bank or local register bank). Both ‘Rw’ and ‘Rb’ require four bits in the instruction
format. The base address of the global register bank is determined by the contents of
register CP. ‘Rw’ specifies a 4-bit word GPR address, ‘Rb’ specifies a 4-bit byte GPR
address within a local register bank or relative to (CP).
reg:
Specifies direct access to any (E)SFR or GPR in the currently active context (global
or local register bank). The ‘reg’ value requires eight bits in the instruction format. Short
‘reg’ addresses in the range from 00
H
to EF
H
always specify (E)SFRs. In that case, the
factor ‘
∆
’ equates 2 and the base address is 00’FE00
H
for the standard SFR area or
00’F000
H
for the extended ESFR area. The ‘reg’ accesses to the ESFR area require a
preceding EXT*R instruction to switch the base address. Depending on the opcode,
either the total word (for word operations) or the low byte (for byte operations) of an SFR
can be addressed via ‘reg’. Note that the high byte of an SFR cannot be accessed via
the ‘reg’ addressing mode. Short ‘reg’ addresses in the range from F0
H
to FF
H
always
specify GPRs. In that case, only the lower four bits of ‘reg’ are significant for physical
address generation and, therefore, it is identical to the address generation described for
the ‘Rb’ and ‘Rw’ addressing modes.
bitoff:
Specifies direct access to any word in the bit addressable memory space. The
‘bitoff’ value requires eight bits in the instruction format. The specified ‘bitoff’ range
selects different base addresses to generate physical addresses (see
). The
‘bitoff’ accesses to the ESFR area require a preceding EXT*R instruction to switch the
base address.
bitaddr:
Any bit address is specified by a word address within the bit addressable
memory space (see ‘bitoff’) and a bit position (‘bitpos’) within that word. Therefore,
‘bitaddr’ requires twelve bits in the instruction format.