TM 11-5895-856-34-1/EE640-CA-MMI-010/E154 CPU/TO 31W2-2T-122-1
serial input line and a serial output line. The computer
interrogate the MTC to determine its status. This status
puts the TTYC into an input mode to accept keyboard
interrogation is augmented by the MTC presenting
input messages to the computer or into an output mode
status each time it interrupts following completion of a
to accept computer messages for printing. Seven-bit
command. Fault detection capabilities incorporated in
ASCII characters (plus 1 bit, odd parity) are sent with
the magnetic tape subsystem interface include loop test,
appropriate start and stop bits as the TTYC-to-TTY
I/O parity error, longitudinal redundancy checks (LRC)
serial interface. Data is transmitted at a 30-character-
and tape parity. Loop test allows software to ensure that
per-second rate for the AN/UGC-74(V)3. The TTYC
the I/O interface is working. Checking for I/O parity
operates in the byte mode, transferring characters to or
error occurs on all bytes of I/O data. All data transfers,
from the TTY. The TTYC can be connected to either of
automatic or loop test initiated, are monitored. The
the two computers by signals contained in a dual-
MTC generates and checks the LRC bits at the end of
channel switch interface. This is a logic connection
each record on the tape. Each byte within the record
which places the TTYC on-line to either computer but
has a parity bit generated and recorded; thus parity is
never to both simultaneously. If neither computer is
checked over the I/O interface and again between the
selected on-line, the TTYC is off-line to both and it will
MTC and MTT. Whenever a Timing or Write Parity
neither send nor receive signals.
error is sensed, the computer is interrupted and the type
of error is presented in the status word. Detected parity
errors on read operations are not reported until inter-
2-20. Line Printer Controller
record gap (IRG) is encountered. The MTCs are dual
The line printer controller (LPC) provides the interface
port devices with an IOE interface to each processor.
between the line printer and the computer. Demands for
While each MTC is logically connected to only one
a character from the printer are relayed to the computer
processor at a time, it may be switched to either, via a
by the LPC. The LPC provides a means for the
manual or logic switch. This allows the MTCs to be
computer program to interrogate the status of both the
switched to the off-line computer for additional data
printer and the LPC. Data output to the LPC is in the
processing, or all units to be placed on-line to the
byte mode. The LPC also alerts the computer program
alternate computer during a switchover.
to parity errors detected in the data output. Proper
functioning of the LPC is checked by a program-initiated
2-19. Teletypewriter Controller
self-test sequence. The LPC is connected to the
computer by means of an IOE interface. Functional
The teletypewriter controller (TTYC) provides the
organization of the LPC is shown in the block diagram
interface between the IOE and an externally buffered
AN/UGC-74 (V) 3 Teletypewriter (TTY). The TTY has a
2-8
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