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BRANCHING
•
In compatibility mode, a branch can
'be executed from bits Rl, R2, or R3.
•
A branch on GMWM can be executed.
Certain branch conditions normally avai-
lable in the 2030 are replaced bydH-
ferent branch conditions when the 2030
is operating in compatibility mode.
These changes are shown in the following
table:
COltlEatibilitI
Mode
2030 Mode
g
g
Rl
1
BC
0110
R2
Sl
1000
R3
G2
1100
GMWM
V67=0
0011
The Rl, R2, and R3 branches are made
from the contents of the R-register.
These branches can be given in the cycle
immediately following a read cycle.
A
GMWM latch has been added that detects a
GMWM On the storage sense bus when a
read cycle occurs.
The GMWM latch feeds
the stat use decoder and remains latched
cn until the next read call is given to
core storage.
I/O OPERATIONS
•
All I/O operations in compatibility
mode are executed in burst mode.
•
The 1402 reader automatically feeds
5-20
•
•
•
a card 6 milliseconds after a read
command.
A stacker select command for the
1402 must be given within 6 millise-
conds after a read command.
End of file occurs with channel end
of the last card read.
Character representation to and from
I/O apparatus is in EBCDI code.
All 1400 systems
1/0
operations are
executed in burst mode.
Tape and file
operations always force burst mode on
the multiplex channel (compatibility
mode included).
Burst mode for 1402 and
1403 operations is forced in the 2030 by
holding up Select Out until Channel End
occurs (Figure 5-12).
The normal resets
of Select Out in 2030 mode is blocked by
the line -Not 1401 Mode."
The only
resets available to turn off Select Out
are Recycle Reset, Select In, or the
micro-program statement R->FB.
Recycle
Reset is the result of giving a system
reset or a recycle reset when in CE
mode.
In compatibility mode, Select In
from the channel can come up only due to
an abnormal condition existing, such as
having
leu
power turned off, or a
machine failure.
Therefore, the only
controlled reset to Select Out will be
the micro program statement R->FB, which
is given when a Channel End is sensed by
the 2030.
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