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Non-Motion Control Commands
No-Operation (NOP)
Mode Set 1 (MS 1)
•
Mode Set 2 (MS 2)
Non-motion control commands do not move tape and do not transfer data across
the channel/ tape control interface.
Channel End and Device End are signaled when non-motion control commands
are accepted (initial status). Non-motion control commands are:
No-Operation
Mode Set
1
Mode Set 2
Diagnostic Mode Set (maintenance aid*)
* Diagnostic programs issue maintenance aid commands via SIOs (op-codes in
the
CCW).
NOP
performs no function in the tape control or tape unit, and does not transmit
data or move tape. No-Operation does not reset tape control sense data.
Programming Note:
Placing a
NOP
command at the end of a series of chained
commands delays channel disconnect. from the tape control until the
NOP
is
executed. Channel operation will be more efficient if this programming
convention is not used.
Mode Set
1
commands sent to tape controls with the seven-track
NRZI
feature
establish tape unit operating mode for succeeding seven-track
NRZI
operations.
Bits 0 and 1 control density and bits 2, 3, and 4 control parity (odd or even),
data converter (on or off), and translator (on or off) circuits in the tape control.
See Figure 6.
A Mode Set 1 command affects operation of all seven-track tape units attached
to the tape control. Unless reset, the tape control retains its mode setting until it
receives another Mode Set 1 command.
Mode Set 2 commands sent to a 3803 Model 2 with the nine-track
NRZI
feature
set operating mode (6250
BPI,
1600
BPI PE,
or 800
BPI
nine-track
NRZI)
for
succeeding write-type operations.
Unless reset, the tape control retains its mode setting until it receives another
Mode Set 2 command.
Diagnostic Mode Set (OMS)
DMS causes an artificial signal-loss condition that checks read and write error
detection circuits.
• In 6250
BPI
Write track P is made all zeros and the program supplies the error
correcting code as part of the data. In 6250 mode Diagnostic Read inhibits
single and double track error correction and sends check characters to channel
with data.
• In
PE
mode, whenever write data contains successive one bits in any. track,
writing in that track is inhibited until the last one bit is reached.
• In
nine-track
NRZI
mode, no bits are written in track P.
• In
seven-track
NRZI
mode, no bits are written in track C.
A Diagnostic Mode Set command affects only operations for the command chain
in which it is issued.
·
Section 2: Commands and Instructions
27
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