Relays, Memory Areas and Constants
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1.3.9 Index Registers (IX, IY) (for FP0, FP−e)
Function of index registers (IX, IY)
Index registers are used to indirectly specify constants and memory area addresses.
Two 16−bit registers are available, IX and IY. Changing addresses and constants using
a value in an index register is called “index modification”.
With the FP0, FP−e, index modification is possible only with regard to operands of
high−level instructions.
Modifying an address
Address = Base address + Value in IX or IY (K constant)
Example: Modifying DT11
IXDT11
Base address IX value Target address
11 + K0 = DT11
11 + K10 = DT21
11 + K−10 = DT1
Modifying a constant
Constant = Base value + Value in IX or IY
Example 1: Modifying K100
IXK100
Base value IX value Constant
K100 + K0 = K100
K100 + K10 = K110
K100 + K−10 = K90
Example 2: Modifying H10
IXH10
Base value IX value Constant
H10 + HA = H1A
H10 + H10 = H20
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