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through 3.
The parity for the X-
register is determined by the parity
lines of both the Hand
J
switches.
Switch H lines 0 through 3 and switch
J
lines 0 through 3 set the XO through X7
positions, respectively.
UV..,>WX is
a
statement in micro
programming that brings up control lines
to gate the U- and V-register to set
ROAR.
The U-register positions
3
through 7 control the W-register.
The CN control field, which is part
of every ROS word, sets the XO through
X5 positions of ROAR and provides parity
on the X-register.
A priority is an interruption of a
micro program routine.
There are nine
orders of priority and each sets one
specific position of the X register.
The position that is set in the X- reg-
ister determines the starting address of
a micro program to handle that particu-
lar interruption.
The priorities and
the positions of ROAR that are set are
listed:
Priority
S'IOP
PROTECT
WRAP
MPX Share
SX Chain Pulse
Machine Check
Initial Program Load
Force
IJ
Machine Reset
ROAR Position
xo
Xl
X2
X3
X4 see
~
X5
X6
X7
XP
Note: Other positions of X may
be
set
in combination because of specific
conditions.
The CH and CL control fields are
decoded to test for branch conditions.
The conditions that are tested determine
how the X6 and X7 positions are set.
Recall that each micro program step
is addressed by a 4-digit number in
hexadecimal.
Let's try an example.
Assume that the ROS cycle that is active
is decoding the ROS word at
address 0123.
If the next address to be
executed in the program is 0225, what
3-62
positions of ROAR are changed and how
might they be changed?
ADDRESS
ROAR
W Position
X position
Register
Positions
= 3
4567
0123
4567
123
in hexadecimal = 0
0001
0010
0011
225
in hexadecimal
=
0
0010
0010
0101
First: The W portion of ROAR has to
be changed from 0001 to 0010.
One way
to set the W-register might be to use
the mnem.onic j(->W.
The CR control field
would be coded 0010.
Remember, the
address 0225 must be set up while
address 0123 is being executed.
Second: The X-register positions 0
through 5 have to be changed from 001000
to 001001.
The CN field of ROS word
0123 must, therefore, be coded 001001.
Last: The X6 and X7 positions of ROAR
are controlled by the CH and CL fields.
The CH field must be coded 0 and the CL
field must be coded
1
to satisfy the
relnaining ROAR positions.
Now that you have seen some of the
ways that ROAR can be set, refer to
Figure 3-40 (j).
This portion of the
figure shows another W- and X register
which is used for indicating purposes.
Because of timing considerations the
output from ROAR is gated to the indi-
cating ROAR to control console lights.
Refer to Figure 3-40
@.
These two
registers, GWX and FWX, are backup reg-
isters for RCAR.
As an example: If
during a step of a micro program the
selector channel has to break in, the
address in the W- and X-registers is
stored in the GW an GX registers.
An
'address will be set into Wand X that is
the first step of another micro program
to handle the interruption.
After the
selector channel roicro prograro is com-
plete, the address that was stored in GW
and GX is returned to ROAR and the orig-
inal program continues.
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