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order bit of the result Z(18).
The zero FF (ZFF) stores the status of the entire result Z(l-18).
The even FF (EFF) stores the status of the low order bit Z(l) of the result. The results of an
operation is available for test on the next instruction. When the branch is based on contents
of the C-register, only Z(l-7) are reflected in ZFF and EFF. When the branch is based on
the internal status lines, only Z(l-10) are reflected in ZFF and EFF.
Plus Flip-Flop (1 bit, PFF, A)
The PFF records (for testing) the condition of Z(18) at the end of an instruction.
If
Z(18} was
zero, the PFF would be plus; but
if
Z(18} was one, the PFF would be minus. The notation Z(18}
refers to bit position 18 of Z -- that is, the high order position of Z.
Zero Flip-Flop (1 bit, ZFF, A)
The ZFF records (for testing) the condition of Z at the end of an instruction.
If
all of the Z
drivers we:re zero, the ZFF would be zero; but if any one of the Z drivers were non-zero, the
ZFF would be non-zero.
Even Flip-Flop (1 bit, EFF, A)
The EFF records (for testing) the condition of Z(l) at the end of an instruction.
If
Z(l) was
zero, the EFF would be even; but
if
Z(l) was one, the EFF would be odd.
On double length instructions (AMD, LDD, STD) the branch flip-flops indicate the following:
Mor A
1
18
M+l or B
~
~
Thus the last word through the Z drivers can be tested for being:
1.
Plus or minus (sign bit)
2.
Odd or even (numerical sense)
3.
All zeros or not all zeros.
Insert Switches (18 switches, S, A)
The switches are located on the control console and are described in the discussion of the
control console. They can be gated in under program control.
[IDruu&~~uc:J ~@------------
I-13
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