Xerox 7120 Reference Manual page 13

ERROR CONDITIONS
The card reader is capable of detecti ng and reporti ng the
following error conditions to the controlling system: incor-
rect length, inval id EBCDIC punches, data overrun, and
read veri fy (Mode I 7140-02) errors.
INCORRECT LENGTH
Incorrect length is caused by the card reader encountering
end of card prior to the "count done" signal from the con-
trolling system or by the occurrence of the "count done"
signal prior to reading column 80 of the card. Thus, ex-
actly 120 bytes must be requested for the binary read mode
and exactly 80 bytes must be requested for the EBCDIC read
mode; otherwise, an incorrect length condition will be sig-
naled to the controlling system. However, the card is al-
ways directed to the stacker specified by bits 2 and 3 of the
Read order.
INVALID EBCDIC PUNCHES
When the card reader has received a Read Automatic order
and column 1 of the card does not have punches in rows 1
and 2, any punch configuration (including column 1) that
cannot be converted into 8-bit EBCDIC (i.e., more than
one punch in rows 1-7) is considered inval id. Detecting an
invalid EBCDIC punch configuration causes the card reader
to generate eight zeros as the data for the invalid column
and to request the controlling system to check parity, in
which case the controlling system sets its Transmission Data
Error indicator to 1. (Xerox 530 and Sigma 2/3 indicate
validity errors by setting the parity error (E) flag in the odd
channel register, not the transmission data error (TE) flag in
the even channe I register.)
If
the Read Automati corder
specified error stacking, an invalid EBCDIC punch config-
uration causes the card to be di rected to a I ternate stacker 2
(Model 7120) or the alternate stacker (Model 7140).
DATA OVERRUN
A data overrun (rate error) is defined as failure of the con-
trolling system to service the card reader at the required
data transfer rate. If the Read order specified error stacking,
a data overrun causes the card to be directed to al ternate
stacker 2 (Model 7120) or the alternate stacker (Model 7140).
READ VERIFY (MODEL 7140-02)
A read verify error is caused by fai lure of the card reader to
read the same data at both read stations. If the Read order
specified error stacking, a read verify error causes the card
to be directed to the alternate stacker.
NOT OPERATIONAL CONDITIONS
A "not operational" condition, generally, is any condition
that causes a peripheral device to switch to the "not opera-
tional" state. For the card reader, any of the following
fault conditions (singly or in combination) may occur during
a card read cycle:
1. Read station malfunction.
2. Transport mechanism malfunction (i.e., card jam).
3. Absence (or failure) of ac and/or dc power in the
reader.
CARD READERSTATUS RESPONSE
The card reader system is capable of returning various status
flags in response to computer-executed I/O instructions.
Detailed explanations of the input/output instruction to re-
quest status of the card reader are contained in the reference
manuals for Xerox computers. The following paragraphs
explain the significance of each status flag returned to the
contro II i ng system by the card reader.
1/0 INSTRUCTION STATUS BITS
The execution of an I/O instruction by the controlling sys-
tem provides two bits of immediate information pertaining to
the general status of the addressed I/O device and its con-
troller. This information is retained by the controlling sys-
tem in a form that allows for conditional branching based
on the response to the I/O instruction. Table 5 lists the
I/O instructions, the possible status bit settings provided by
each I/O instruction, and the significance of each setting.
DEVICE STATUS BYTE
Eight bits of information in the Device Status Byte are made
avai I able to the computer in response to the execution of an
I/o instruction, as shown in Tables 6, 7, and 8.
OPERATIONAL STATUS BYTE
In addition
t~
the information contained in the Device
Status Byte, the Operational Status Byte generated at the
end of each I/O operation a Iso provides i ndi cators to the
controlling system (see Table 9).
PROGRAMMING CONSIDERA liONS
SEQUENCE OF ACTIVITY
Figure 3 illustrates the sequential relationship of the key
events that occur during a card reading operation.
TIMING INFORMATION
Figures 4, 5, 6, and 7 illustrate the time-dependent events
occurring during a card reading operation for the respective
models.
Card Reader Status Response/Programming Considerations 7