IA88C00
Microcontroller
Data Sheet
As of Production Version -01
Copyright
2005 ENG 21 0 050519-00 www.Innovasic
Innovasic.com
Innovasic Semiconductor
Page 16 of 80 1.888.824.4184
1. High order bit of the 4-bit address selects one of the two register pointers (0 selects RP0; 1 selects RP1).
2. Live high order bits in the register pointer select an 8-register (contiguous) slice of the register space.
3. Three low order bits of the 4-bit address select one of the eight registers in the slice.
The process results in linking together the five bits from the register pointer to the three bits from the
address to form an 8-bit address. The three bits from the address will always point to an address within
the same eight registers, as long as the address in the register pointer remains unchanged.
Changing the five high bits in control registers R214 for RP9 and R215 for RP1 allows the register
pointers to be moved.
Using full 8-bit addressing allows the working registers to be accessed. The lower nibble is used similarly
to the 4-bit addressing described above when an 8-bit logical address in the range 192 to 207 (C0 to CF)
is specified. This is shown in section b. of Figure 8.
Together They Create 8-Bit Register Address
Selects RP0
or RP1
RP0 (R214)
RP1 (R215)
Address
Opcode
Register Pointer Provides
Five High-Order Bits
4-Bit Address Provides Three Low-Order Bits
a. 4-Bit Addressing
Selects RP0
or RP1
RP0 (R214)
RP1 (R215)
Address
Register Pointer Provides
Five High-Order Bits
b. 8-Bit Addressing
8-Bit Physical Address
1
1
0
0
8-Bit
Logical
Address
Three Low-
Order Bits
Figure 8. Working Register Window
Physical registers 192 to 207 can be accessed only when selected by a register pointer. This is because
any direct access to logical addresses 192 to 207 involves the register pointers. After a reset, RP0 points
to R192 and RP1 points to R200.