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Transmission errors may be detected by using a bit buffer with full duplex line in the following
manner.
A bit buffer has the capability of echoing what is received. This is controlled by activating the
appropriate instruction and, therefore, is under program control. When echoing, the bit received
by the receive section is retransmitted over the transmit portion of the full-duplex line. In this
way, a terminal device with error control capability can verify what was received by the DATANET-
30 (actually, what is received back by the terminal device). Whenever a bit buffer channel is set
up for echoing, the transmit section is locked out so that the bit ordinarily in the transmit data
buffer cannot interfere with what is being sent back to the terminal device.
The usual equipment at the transmitting end is a keyboard printer send/receive unit. The infor-
mation is transmitted in the normal manner but the printer does not print a hard copy as a direct
result of the transmission.
The transmitted signals are received by the receive section of a bit
buffer and immediately transmitted back to the page printer of the transmitting terminal. Thus,
the printed information indicates the number of possible errors involved in the transmission of
the message.
This technique quickly shows whether or not the lines are working properly and in the case of an
administrative message, whether or not it is possible to "read thru" the errors.
If
the errors are
too high, the transmitting terminal can take appropriate action.
If
the transmission contains
important numerical data where the numbers must be correct, the transmitting station again can
immediately verify that the transmission was satisfactory.
The Character/Word Unit Module (CWU 930)
The character/word unit module occupies one module space and can contain either two Character
Buffer Channels (CBC), two Word Buffer Channels (WBC), or one of each. The buffer selector
address of each CBC or WBC is specified by the wiring of the address plug for the module, and
each may be addressed independently of the other.
DATANET-30
cwu
WBC
DATANET-30
cwu
WBC
CBC
Fi£rure 15. Character/Word Buffer Channel
REMOTE
TERMINAL
[ID£1J&~~1JCJ ~®------------
-23-
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