Xerox 7120 Reference Manual page 9

CARD READER STATES
The initial state of the card reader depends on its power
status. The complete absence of power to the card reader
subsystem (that is, the absence of its prime ac power and
system dc power) effectively removes the card reader from
the control I ing system.
All attempts to access the card
reader result in a response of "no input/output address rec-
ognition" to the I/O inshuctions. Furthermore, unpredictable
status conditions are suppl ied if status response is requested
by the I/O instruction. In the absence of ac power, the
presence of system dc power will enable address recognition,
but the card reader assumes a "not operational" state. L ike-
wise, failure of power supplies internal to the card reader
causes the card reader to assume a "not operational" state.
OPERATIONAL STATES
The presence of ac and dc power, with no read station faul t
or transport mechanism fault, enables the card reader to as-
sume either of two device conditions ("ready" or "busy")
and either of two modes ("manual" or "automatic"). A read
station fault exists if one or more of the photoelectric
channels for sensing punches in the card rows have failed to
pass the read station test in the previous card read operation.
A transport mechan ism faul t exists if a card jam exists in any
portion of the card transport area.
The exact condition and mode status of the card reader at
any given time is returned to the controlling system in re-
sponse to such I/O instructions as SIO, HIO, and
no.
Other I/O instructions, such as AIO and TDV, provide more
specifi c indications of the card reader's status (see "Status
Response" in Chapter 3). Abriefexplanationofthepossible
conditions and modes of the card reader follows.
CONDITIONS
Ready. In the" ready" condition the card reader is capabl e
of accepting an SIO instruction, providing no device inter-
rupt is pending. In order to be in the "ready" condition,
the card reader must be operational (that is, all conditions
defined under "Operational States" must be satisfied) and
the execution of an order to read a card is not in progress
or pending.
Busy. In this condition the card reader has accepted an SIO
instruction. The unit will not accept a new S10 until the
current order list is completed and no device interrupt is
pending.
MODES
Manual. The card reader assumes the "manual" mode when
any condition arises requiring operator intervention before
the reader can function normally (e.g., stacker full, hop-
per empty, etc.). The "manual" mode is forced by the
operator pressing the STOP switch or RESET switch on
the card reader control panel. The reader can accept an
SIO instruction in this mode, but will not act on it in any
way until it enters the "automatic" mode.
Automatic. When all necessary conditions for successful
card reader operation are present, the reader is placed in
the "automatic" mode by the operator pressing the START
switch on the card reader control panel (thus illuminating
the switch).
TRANSITION BETWEEN STATES
The allowable card reader state transitions and the condi-
tions causing the reader to change from one state to another
are summarized in Table 2.
DATA TRANSFER
A card read operation is initiated by the controll ing system
with a START INPUT/OUTPUT (SIO) instruction if all the
following conditions are satisfied:
1. Input/output address recognition exists.
2. The card reader is in the" ready" condition.
3. No interrupt is pending.
If the card reader is in the "automatic" mode, it then requests
an order from the controll i ng system. After accepting a read
order, the card reader advances a card from the input hop-
per to the read station, and commences to read the card,
column by column, beginning with column 1. If reading is
performed in the EBCDIC mode, one 8-bitbyte is transmitted
to the control I ing system for each col umn read, and a code
validity check is performed on each byte. In the binary
read mode three 8-bit bytes are transmitted to the control I ing
system for each odd-even-numbered pai r of col umns (no
val idity check is performed in this mode). Reading continues
until one of the following conditions occurs:
1. The end of the card is detected.
2. The card reader receives a "count done" or "halt" sig-
nal from the controlling system.
3. A "fault" condition is encountered.
If the card read operation was not terminated by a card jam,
the card is then routed to the stacker station, where it is
sensed and directed to the normal stacker unless:
1. The Read Automatic order specified error stacking and
the validity check (for EBCDIC mode only) indicated
that the card contained an invalid EBCDIC punch con-
figuration, in which case the card is directed to alter-
nate stacker 2 (Model 7120) or to the alternate stacker
(Model 7140).
2. The Read order specified error stacking and a data over-
run has occurred, in which case the card is directed to
al ternate stacker 2 (Model 7120) or the alternate stacker
(Model 7140) and the controll ing system is notified of
the error with the Data Overrun and Unusual End
indicators.
Card Reader States/Data Transfer 3