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REY
•
A display o.f four bits plus parity.
•
Indicates the main storage protec-
tion key for all commands associated
with the start I/O instruction.
COMMAND
•
These four bits, when decoded, iden-
tify the channel command.
FLAGS
•
This group of five indicators dis-
plays the manner in which a channel
command is executed.
•
These indicators, when on, have the
following meaning:
TAGS
•
6-6
CD
Indicates chaining of data
addresses
CC
Indicates command chaining
SLI
Indicates that the program
will not be notified in the
event of wrong length record.
SRIP
This bit is turned on when it
is desired to inhibit writing
data into storage during Read,
Read Backwards, or Sense oper-
ations.
PCI
This is the Program Controlled
Interrupt bit, which permits
the channel to generate an
interrupt upon fetching the
CCW.
Nine selector channel tags are dis-
played as follows:
OP IN-Indicates that an I/O unit has
been selected and is in COIHlluni-
cation with the channel.
ADDR IN- Indicates that the address
of the currently selected I/O
unit is on Bus In.
STAT IN - Indicates that the select-
I/O unit has placed status infor-
mation on Bus In.
SERV IN - Indicates that the select-
ed I/O unit is ready to transmit
or receive data.
SEL OUT - When this light is on, the
several I/O units are being
polled to determine which unit
requested service.
ADDR OUT - Indicates that the infor-
mation on Bus Out is an address.
CMND OUT - Indicates that the infor-
mation on Bus-Out is a command.
SERV CUT - Indicates that the CPU
has accepted the information on
Bus In or has provided data on
Bus Out.
SUPP OUT - This Signal used alone or
with other tags indicates the
following functions:
Suppress Status
Suppress Data Transfer
Chained Command Control
Selective Reset.
CHECRS
•
Indicates a detected malfunction
during selector channel operation.
•
The Check lights are turned on for
the following reasons:
IL - This light is turned on whenev-
er the number of bytes con-
tained in the assigned storage
area is not equal to the number
of bytes requested or offered
by the I/O unit, provided the
SLI flag is not on.
PROG - When this light is on, the
channel has detected a program-
min9 error.
PROT - This light is turned on
whenever the channel attempts
to violate a protected area of
Main Storage durin9 an I/O
operation.
CHNL DATA and CHNL CTRL - Any time
an invalid byte of data is
detected in the data register,
the CHNL DATA Check light is
turned on.
If a control byte
is contained in the data reg-
ister at the time the error is
detected, the CHNL CTRL Check
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