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Data Communications
COMPUTER
TERMINAL
"I'd 1
0
k
d
0
f
. "
HI
~
I
e you to sen me some In ormation. - - - ESCd - - - - - - - -.....
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..And I'd
like
it
ri:~;~OW!
.. -
DCl
I
:
i
~
then
I
i'
' - The next block of information is transmitted.=============~
Figure 5-3. Block Transfer Enabled By The Computer
NOTE
The computer should not be allowed
to echo back information that has
been transmitted as a block from the
terminal.
BLOCK MODE
When the terminal is in Block Mode (BLOCK MODE key
down) characters are not transmitted as they are typed.
Instead, the user can input data to the terminal, then edit
and correct the data before sending it to the computer
using the ENTER key. The data can be grouped into con-
venient blocks, either lines or pages (refer to the config-
uration procedures later in this section). Block Mode oper-
ation allows you to efficiently utilize computer and com-
munication facilities.
The G and H switches on the Keyboard Interface PCA are
used to control the terminal's response to block transfer
requests (refer to table 5-8).
Switch
Setting
Block Operation
G
H
Closed
Closed
Data transfers used DC1/DC2 handshake. Other trans-
fers are triggered by the receipt of a DC1 character.
Closed
Open
Data is sent when the . . key is pressed. Other
block transfers are triggered by the receipt of a DC1
character.
Open
Closed
All block transfers require a DC1/DC2 handshake.
Open
Open
No DC1/DC2 handshake is required for any block
transfer.
Note: In half duplex operation, a line turnaround is substituted for a DC1
character.
The size of the block of information transferred in BLOCK
MODE, and the control characters used to separate fields
and to terminate blocks differ somewhat, depending on the
Line/Page Strapping of the terminal and whether or not
the terminal is operating in FORMAT MODE. Figure 5-4
illustrates these differences.
In the example in figure 5-5, the user has an application in
which order data is to be entered in the same
for~at
as a
standard company form.
FULL DUPLEX OPERATION
In full duplex operation, the characters which are typed at
the keyboard are transmitted to the computer and are not
displayed unless they are returned by the computer. This
setting is ignored when in Block Mode.
TELETYPE COMPATIBLE COMMUNICA-
TIONS
In teletype compatible (full duplex, character mode) appli-
cations, the terminal can be quickly configured for use by
following the instructions given in the Installation sec-
tion. Note that if block data transfers are used the com-
puter should be programmed to use the simple DClIDC2
protocol described under Multicharacter Transfers.
5-9
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