IBM 1 Series - Types of Receive Operations

Types of Receive Operations
Prior to presenting the following sections, it is important to distinguish
between the two types of receive operations that the teletypewriter adapter
performs:
e A Normal Receive Operation. This is a receive operation that results in
the posting of an attention interrupt. No data characters are lost.
e An Overrun Receive Operation. This is a receive operation that results
in the posting of an exception (overrun) interrupt. A second character
was received and the leading edge of the first stop-bit time for this
second character was detected before the first character was read by
the program. The second character is lost. The first character is in the
receive buffer register and can be read by executing an Operate I/O
instruction with a Read command in the IDCB.
Teletypewriter Adapter Feature 4-13