Xerox 550 Reference Manual page 135

Interrupt at Channel End (Bit Position 35). An I/O interrupt
may be requested when the device signals a "channel
end" (signifying that the current order has been either com-
pleted or terminated) by coding the Interrupt at Channel
End (ICE) flag as a
1.
If the I/O interrupt level within the
interrupt system (location XISC') is armed, enabled, and not
inhibited, the request will
be
processed by the BP in ac-
cordance with the priority that prevai Is within the interrupt
system, the lOPs, and the I/O subchannels of the MIOP.
The occurrence of an I/O interrupt because of a "channel
end
ll is reported as status information (bit position 11 of
register R) when the BP executes an AIO instruction (nor-
mally part of the I/O interrupt-handling routine). The I/O
interrupt request may be processed without affecting the
I/O operation. (Note: Specific conditions under which a
IIchannel end
ll
signal may be generated are dependent upon
the characteri sti cs of the devi ce. Refer to an appropri ate
Xerox peripheral reference manual for further detai Is. )
Halt on Transmission Error Flag (Bit Position 36). The fol-
lowing errors (or "unusual end" condition) may be detected
by the MIOP when an lOCO is being executed:
1. Bus check fault (BCF) whi Ie fetching data.
2. Transmission Data Error (TDE); may also be detected by
device controller.
3. Transmission Memory Error (TME).
4. Write Lock Violation (WLV), during input operations
only.
5. Incorrect length, conditional; see "Suppress Incorrect
Length Flag".
6. Memory Interface Error (MIERR) whi Ie fetching data.
If
the HTE flag is coded as a
0,
the above errors are recorded
when detected and reported as status information when the
BP executed an SIO, TIO, or HIO instruction, but the I/o
operation is not halted.
If
the HTE flag is coded as a 1, and any error (as listed
above) is detected, the I/o operation is terminated im-
mediately. The error is also reported as status information
when the BP executes an SIO, HIO, or TIO instruction.
The HTE flag must be coded identically in every lOCO as-
sociated with the same logical record. Thus, if data chain-
ing is specified, the HTE flag in the new lOCO must be the
same as the HTE flag in the previous lOCO. This restriction
applies to data chaining only, and not to command chaining.
In addition to the "unusual end" conditions listed above,
which may terminate the I/O operation only if the HTE
flag is coded as a 1, any of the following "unusual end"
conditions wi
II
unconditionally terminate the I/O operation:
1. Memory Address Error (MAE).
2. lOP Control Error (IOPCE).
128 Input/Output Processor (lOP) Fundamentals
3. Control Check Error (CCF).
4. lOP Memory Error (IOPME).
5. Bus Check Fault (BCF) whi Ie fetching an 10CD.
6. Memory interface Error (MIE) while fetching an lOCO.
Interrupt on Unusual End Flag (Bit Position 37).
If
an I/O
Interrupt is to be requested when an "unusual end" condition
is detected whi Ie either fetching or executing an 10CD,
the Interrupt on Unusual End (IUE) flag must be coded as
a 1. If the I/O interrupt level within the interrupt system
(location X I 5C') is armed, enabled, and not inhibited, the re-
quest wi
II
be processed by the BP in accordance wi th the
priority that prevalis within the interrupt system, the lOPs,
and the I/O subchannels within an MIOP. The occurrence
of an I/O interrupt because of an "unusual end" condition
is reported as status information (bit position 12 of reg-
ister R) when the BP executes an AIO instruction (normally
part of an I/O interrupt-handling routine). The I/O inter-
rupt request may be processed wi thout affecti ng the progress
of the I/O operation.
If the IUE flag is coded as a
0,
an "unusual end" condition
may be detected but no interrupt wi" be requested.
Suppress Incorrect Length Flag (Bit Position 38). An incor-
rect length condition may occur when the specified byte
count is not equal to a fixed or prescribed byte count for a
record (e. g., attempting to read more than 80 columns of
data from a punched card). Specific conditions under which
an incorrect length signal is generated are dependent upon
the device. Refer to an appropriate Xerox peripheral equip-
ment reference manua I for further detai Is.
If the Suppress Incorrect Length (SIL) flag is coded as a 0
when an incorrect length condition is detected, it is re-
ported as an incorrect length and, depending upon the de-
vice, may be reported as an "unusual end".
If
the HTE flag
is aiso coded as a I, the I/O operation is terminated and
reported as an "unusual end".
If the SIL flag is coded as a 1 when an incorrect length con-
dition is detected, it is reported as an incorrect length but
suppressed as an "unusual end". Hence, the I/o operation
is not terminated.
The presence or absence of an incorrect length condition
is reported as status information when the BP executes an
SIO, HIO, AIO, or TIO instruction.
Skip Flag (Bit Position 39). If the Skip (S) flag is coded as
a
0,
it has no effect upon the I/o operation.
If the S flag is coded as a 1, the lOP is inhibited from ac-
cessing main memory and consequently no data is transferred
between the main memory and the data buffers of the I/O
subchanne
I.
All other operations or functions within the