Appendix C Table Of Special Function Registers Appendix - Toshiba TLCS-90 Series Data Book

TOSHIBA TMP90C840
(9) Addressing modes for extended data area
The TMP90C840 provides up to 1M bytes of data.
The addresses OOOOOH to OFFFFH can be accessed in a normal addressing
mode.
However, the addresses from IOOOOR to FFFFFH called an "extended data
area" require a special addressing mode for access.
Accessing the extended data area requires to select the addressing
mode which uses the index register IX or IY for obtaining the address
of the operand (the register indirect addressing mode or the index
addressing mode).
The following four special modes are available:
(IX)
(IY)
(IX+d)
( IY+d)
In these modes, the extended data area is accessed by using a 20-bit
address consisting of a 16-bit offset address (address bus AO to A15)
and a bank address (address bus A16 to A19).
The 16-bit offset address is obtained by the same way as in a normal
address computation. The 4-bit bank address is specified by the bank
register BX or BY. The register pair BX is selected when the index
register IX is used, and BY is selected when IY is used.
Example:
LD A, (IX)
Memory
CPU
1
A
45
1<-1------
1 1 45 62000H
1
1
BX
1
6
1
IX
I
2 0 0 0
1 1
---------------------------_1
"45H" in the address 62000H is loaded into Register A.
MPU90-l6