IBM System/360 Operating Guide

Multiplexor-Channel Dis plays
MPX Channel Bus-Out Register
These lights indicate the byte of information being
sent from the main-storage data register (MSDR)
to the multiplexor channel.
MPX Channel Tags
These lights provide display of the current status
of various multiplexor-channel I/O interface control
lines.
OP IN. The operational in (OP IN) lamp indicates
that an I/O unit is selected and is in communication
with the channel.
ADR IN The address in (ADR IN) light indicates
that the address of the currently selected I/O unit
is on bus-in. (Bus-in is the data and control
transmission network for information transfer from
a control unit to the CPU.)
STAT IN. The status in (STAT IN) light indicates
that the selected I/O unit has placed status infor-
mation on bus-in.
SERV IN. The Service in (SERV IN) light indicates
that the selected I/O unit is ready to send or receive
data.
SEL OUT. The select out (SEL OUT) light indicates
that the various I/O units attached to the multiplexor
channel are being polled to determine whether any
device requests service.
ADR OUT. The address out (ADR OUT) light indi-
cates that address information is on bus-out. (Bus-
out is the data and control inform::ttion network from
the CPU to the control unit. )
CMND
OUT. The command out (CMND OUT) light
indicates that the information on bus-out is a
command.
SERV OUT. The service out (SERV OUT) light
indicates that the CPU has accepted the information
on bus-in or has provided data on bus-out.
SUPP OUT. The suppress out (SUPP OUT) light
indicates that status and data transfers are sup-
pressed, that command-control chaining is in
progress, or that a malfunction (selective) reset
is being effected with regard to the selected I/O
unit.
Selector-Channel Displays
Several indicators are provided for each selector
channel. The Channel Number One lights refer to
selector-channel one; the Channel Number Two
lights refer to selector-channel two.
The Count Register (located above the Channel
Number One lights) is used to observe the current
byte count for selector-channel one (switch E set
to GUV-GCD) or selector-channel two (switch E
set to HUV-HCD).
Data Register
Whenever.a main-storage share cycle is initiated
by a channel, these lights provide full-time display
of information being transferred.
Key
These lights provide full-time display of the main-
storage (CAW) protection key for all commands
associated with the Start I/O instruction.
Command,
The four low-order bits of the CCW operation code
are displayed by these lights.
Flags
This group of five indicators displays the manner in
which a channel command should be executed, as
follows:
CD. This light indicates chaining of data addresses.
CC. This light indicates command chaining.
SLl. This light (suppress-length indication) indi-
cates that the program will not be notified in the
event of a wrong-length record.
SKIP. This light specifies suppression of
information-transfer to storage during a read,
read backward, or sense operation.
PCl. This light (program-control interruption)
indicates that the channel will generate an inter-
ruption condition when the CCW takes control of
the channel.
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IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English