IA88C00
Data Sheet
Microcontroller
As of Production Version -01
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.
RP0 (R214)
RP1 (R215)
RP0 (R214)
RP1 (R215)
Selects RP0
or RP1
Selects RP0
or RP1
Address
Opcode
Address
8-Bit
Logical
Address
4-Bit Address Provides Three Low-Order Bits
Three Low-
Order Bits
Register Pointer Provides
Five High-Order Bits
Register Pointer Provides
Five High-Order Bits
1
1
0
0
Together They Create 8-Bit Register Address
a. 4-Bit Addressing
8-Bit Physical Address
b. 8-Bit Addressing
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.
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Innovasic Semiconductor
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