Control Instructions - IBM 7090 Instruction-Reference

Beginning-of-Tape Test BTT +0760 ... XXXX (I, L) Figure 5.3-46
This instruction tests the status of the beginning-of-tape indicator in a particular
data channel. Address 1000-10000 selects data channels A-H respectively. If the
beginning-of -tape indicator for the selected channel has been turned on by a previous
instruction, the indicator is turned off and the computer takes the next instruction in
sequence. If the indicator is already off, the computer skips the next instruction.
End-of-Tape Test ETT -0760 .•. XXXX (I, L) Figure 5.3-46
This instruction uses address 1000-10000 to select the data channel in which the
end-of-tape indicator is to be tested. If the indicator is on, it is turned off and the
computer takes the next instruction in sequence. If the indicator is off, the computer
skips the next instruction.
5. 3. 08 Control Instructions
Control instructions are provided so the programmer may change the problem condi-
tions or service the computer.
Halt and Proceed HPR +0420 (I, L) Figure 5.3-47
This instruction causes the computer to stop at the end of I time. When the start
button is depressed, the computer proceeds to the next instruction in sequence. When
halted, the PC contains the address of the next sequential instruction.
Halt and Transfer HTR +0000 (I, L) Figure 5.3-48
This instruction causes the computer to stop at the end of 1 time by turning on the
master stop trigger at 110(D1). Depressing the start button causes the computer to
proceed in L time of a transfer operation and the computer takes an instruction trans-
fer to location X. When halted, the PC contains the address of the HTR instruction.
No Operation
NOP +0761 (I, L)
The NOP instruction performs no active function, but is used to reserve space for
other instructions. Since this instruction has a primary operation 76, an 1 and an L
cycle are required. The only function of this instruction is to turn on the end operation
trigger to allow the computer to proceed to 1 time of the next sequential instruction.
SOD 01 on Systems 3.07.01. 1 causes L END OP on Systems 8.00.09.1.
Execute
XEC +0522 (I) Figure 5.3-49
This instruction causes the computer to perform the instruction at location X. The
program counter is not altered; therefore, after the instruction at location X has been
executed, the computer proceeds to the next sequential instruction (instruction in next
position beyond the XEC instruction). XEC prevents AR to PC on Systems 3.06.05.1.
If the instruction at location X is an unconditional transfer or a successful conditional
transfer, the computer does not proceed to the next instruction following the XEC, but
proceeds to the address specified by the transfer. Another exception occurs when the
instruction at location X is a skip type, and the conditions are met for this skip. The
PC is stepped and the skip is in relation to the location of the XEC instruction.
Set Sign Plus
SSP +0760 ••• 0003 (I, L) Figure 5.3-50
This instruction places a zero (a plus) in the accumulator sign position. Positions
(Q-35) of the accumulator are unchanged.
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