1989_MELPS_7700_Software_Manual

Relative
Mode
Function
Relative addressing mode
Branching occurs to the address specified by the value resulting from addition of the
contents of the program counter and the instruction's second byte. In the case of a
long branch by the BRA instruction, a 15-bit signed numeric value formed by the contents
of the instruction's second and third bytes is added to the program counter contents.
If the addition generates a carry or borrow, 1 is added to or subtracted from'
the program bank register.
Instruction: BCC, BCS, BEQ, BMI,
BNE, BPl, BRA, BVC, BVS
ex.
: Mnemonic
BCC *-12
Machine Code
9016 F416
Branches to the address * -12 if the carry flag (C)
has been cleared
Memory
Advances to the address * If the carry flag (c)
has been set
Memory
~
Address to be
executed next
Op Code (90,.)
Operand (F4,,)
...... -
~
*
Jump
Address to be
executed next
,.....
Op Code (90,,)
Operand (F4,.)
-
*
ex.
: Mnemonic
BRA 1234H
Machine Code
821634161216
Memory
-
-- -------
Op Code (82,,)
Operand (34,,)
Operand (12,.)
---:-----
Program
Bank Register
~ FF12,.
Program
bank-PG
,,, .. ,, '0 " (
executed next
~1146,.
Program
bank-PG+1
f--------
-
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