DATA 620/i SYSTEM REFERENCE MANUAL . - Al Kossow's Bitsavers

S¢FX
Subtract Overflow from
X Register
Timing: 1 cycle
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 0
f-T- !
L _ -L _ ..L. ______
IIS-bitl
option
00 5 744
...L.....___--I-_________----"'
The contents of the overflow indi cator (OF) are subtracted from
the A (B,X) register, mod 2 16 (2 18 ). The overflow flip-flop
does not change.
Indexing: No
Indirect Addressing: No
Registers Altered: A (B, X)
3.3 DOUBLE-WORD
INSTRUCTIONS
Double-word instructions may be either addressing or nonaddressing.
The instructions of the double-word addressing
group are jump, jump and mark, execute, and extended
addressing.
The instructions. in the double-word non-addressing group are
the immediate instructions.
3.3. 1 Double-Word Addressing Instructions
For double-word addressing instructions, the second word is
contained in the memory location following the instruction
word. The second word may contain an operand or an address.
The address may be either indirect or direct. The general flow
chart for double-word instructions is shown in figure 3-8.
Bits 0 through 8 determine the conditions for execution of the
instruction. The condition is tested if the corresponding bit
is equal to one. For example, if bit 0 equals one, the instruction
wi II exam ine the status of the overflow fl ip-flop. If overflow
is set, the command wi" be executed. If overflow is not
set, the next instruction in sequence will be executed.
Jump instruction group. For the jump instruction group, the
address field A, contains a set of nine flags which define the
logical conditions for execution of the jump function. The
jump address is contained in the second word of the doubleword
instruction. Table G-5 (a), in appendix G, summarizes
the logical condition associated with each bit in the address
3-31