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Data Communications
CHARACTER MODE
In Character Mode operation (BLOCK MODE key up), the
terminal sends characters to the computer as they are
typed. This mode of operation can be used for conversa-
tional exchanges with the computer.
Example:
Computer:
User types:
Computer:
User types:
and so on
Plea5e type your company name
AJAX
What file number would you
like from the AJAX library?
12345
In order for the terminal to make a block transfer, it must
first be enabled and then triggered by the computer.
Transfers are enabled by the ENTER or special function
keys while the terminal is in Block Mode (see figure 5-2).
When a transfer is enabled from the keyboard, the termi-
nal sends a DC2 character to the computer to indicate that
a data block is ready for transmission. (This process can be
modified by strap settings on the Keyboard Interface, refer
to Section VII.) A transfer can also be enabled from the
computer by an escape sequence requesting status (ESC
"), cursor sensing (ESC a), or device control (ESC&p...) as
shown in figure 5-3.
When the transfer is enabled the keyboard is locked out
until the transfer is complete. Enabling sequences should
not be entered from the keyboard or cartridge tapes be-
cause they will cause the keyboard to be locked until the
computer responds with a DCI character..(Ifthe computer
does not respond, a soft reset will cancel the transfer and
re-enable the keyboard.)
MULTICHARACTER TRANSFERS
There are certain functions that always result in mul-
ticharacter (block) data transfers.
•
device input/output and control operations, including
tape transfers
•
special function keys
•
status requests
•
cursor sensing
•
all transfers while in Block Mode
Once a block transfer has been enabled, it must be
triggered by the computer before the block of data is actu-
ally sent. The computer triggers the transfer by sending a
DCI character when it is ready to receive the data. The
terminal also assumes that it has received the trigger
when it is first powered up or fully reset, or when the
REMOTE key is pressed (down).
The computer software must support the handshaking
process used in multiple character transfers. The DC2
character must be recognized as a request to send data and
the DCI character must then be sent to trigger the trans-
fer after buffers have been allocated to receive the data.
Additional software support may be needed depending on
your need for terminal or device control. There are straps
on the Keyboard Interface that can be used to modify the
handshaking process. These are discussed later in this
section.
COMPUTER
r
"let me know when you've got some information for me." - DC1
}
TERMINAL
later
Enable
HI
~
--.-
="Hey. I'm ready to send you some information!" - DC2 (ENTER
key)~
then
.....
~ ~'
. - "O.K., I'm ready to receive your information." -
DC1------------~!!!!!!!!!!!!!!!!!!!!jll
\ . .
then
A block of information is transmitted
•
Figure 5-2. Block Transfer Enabled By The ENTER Key
5-8
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