Data Transmission - IBM Series 1 User Manual

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GENERAL DESCRIPTION
Datg Transmission
Data is transmitted and received by the teletypewriter
adapter serially by bit. Data is transferred one 8-bit
character at a time. Each data character is preceeded by
one
st~~!
bit and is followed by one or two §!Q£ bits.
Characters being transmitted from the teletypewriter adapter
to an OEM device are always followed by two stop bits.
Characters being received
by the teletypewriter adapter
may
have one or two stop bits. A start bit is always a
spac~
or
logical zero, and a stop bit is alvays a mark or logical
one. The transmit and receive lines are always held in the
mark state when no data is being transferred. Figure 4-2
shows the format of an eleven bit transmitted or received
character frame.
The teletypewriter adapter is a full duplex attachment.
Data can be transmitted and received concurrently. OEM
devices attached to the teletypewriter adapter should be
configured for full duplex operation.
No error checking is done on transmitted or received
data. The teletypewriter adapter is code transparent. All
256 combinations of 8-bit characters can be transmitted or
received.
It is not possible to overrun on data be~ng transmitted
by the teletypewriter adapter.
It is possible to overrun on
data being received by the teletypewriter adapter. If a
second character is received before the first character is
serviced
by
the software, the first character wil.,! nol be
lost, but the second character
vi!!
be lost.
Figure 4-2. Format of an l1-bit transaitted or received
character frame
11
Start bit
~
I
!~T:T5--i-~T;-:-2Tl--:-~-i St~~---~
LJ : : : : : : ' :
bit(s) :
' - - - _L. ___
..! ___
!.. ___ , ___ .J ___
..! _ __
.! ____ , .' ___
oJ
II
'------.__-----","-v-'"
m
11
The line is always held in a 'mark' condition when
no data is being transmitted.
II
The start bit is always a 'space' (logical zero).
1' 1
Eight data bits are transmitted for each character.
Each bit is either a mark or a space, depending on
the character code. Note that the least significant
bit is transmitted rust.
II
The stop bit is always a mark (logical one). On
transmit, two stop bits are always used. On receive,
one or two stop bits can be used.
Teletypewriter Adapter 4-9