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A single parity bit is assigned to two characters in the
2845 buffer storage. As a result, if a buffer parity error
is detected within the 2845, two Check symbols are dis-
played on the 2265 screen since' either character. may be
in error. See Figure 3. Due to the storage method used,
these Check symbols appear exactly eight lines apart in
the 15 x 64 display format (6 lines apart in the 12 x 80
display format) and in the character positions immedi-
ately following the characters in which the parity error
occurred. If either of the display positions following the
possible characters in,error contains a character, the
Check character will replace that character. If the 15 x 64
display format is used, a parity error occurring in the
eighth display line will display one Check character on
that line only. A second Check character is not displayed
elsewhere on the screen since no 16th line is displayed.
Upon display of the Check characters, the keyboard is,
in effect, locked. That is, the next attempted keyboard
entry locks the keyboard, and the character is not entered
into the display buffer nor displayed. Thus the operator
receives a positive indication that an error has been
detected. Following operator verification of the cause of
the locked keyboard, the keyboard maybe restored
(unlocked), and keyboard entry resumed, by depressing
the RESET key.
IPROGRAMMING NOTE: If a Read Addressed Full DS Buffer
command is begun before the keyboard has been stored (RESET
key depressed), a CAN character is automatically transmitted
following the display buffer contents. No CAN character is trans-
mitted if the RESET key is depressed before the read buffer oper-
ation is started. When an internal parity error is detected by the
2845 in any character stored in the display buffer, the error is
identified by display of the check character. If an internal parity .
error is detected after the ENTER key
is
depressed and the Display
Station is polled, the CAN character is transmitted following the last
character of text. CAN is transmitted even though the parity error
did not occur in one of the characters of the Display Station message.
The operator may intervene at any time after the ENTER key is
depressed but before a poll command is recognized by the 2848 if a
check character is noted on the display screen. By depressing the
RESET key, the operator interrupts the Enter operation. If the
character in error is not included in the Display Station message
(error affects other data displayed on the screen), the ENTER key is
again depressed. These actions prevent the CAN character from
being transmitted in the message. However, if the check character
appears in the Display Station message, the operator may correct
the error by inserting the proper character and again depressing the
ENTER key.
CONTROL KEY FUNCTIONS
The actions that occur when certain control keys are
depressed are described in Tables 1 and 2 for both the
nondestructive and destructive cursor. The display
symbols associated with control key functions, where
applicable, are as follows:
.
1. SaM symbol
~
2. NL symbol
~
3. Nondestructive cursor _ : This symbol is displayed
immediately below the next displayable position, thus
ABC _
. If the D character key is depressed, the
new display will appear as ABCD _
.
4. Destructive cursor -: The small horizontal bar is the
destructive cursor symbol and denotes the next
available display position, thus ABC - . If the D
character key is depressed, the display will appear as
ABCD-
The control keys, described in Tables 1 and 2, all
appear on 2265 Display Station keyboards even when the
feature associated with the key is not installed in the
associated 2845 Display Control. For example, the PRINT
key is present on the 2265 keyboard even though the
attached 2845 is not equipped with the Printer Adapter
feature. The data in Tables 1 and 2 for each control key
includes a description of the effect of depressing the key
when the associated feature is not present.
2265 DISPLAY STATION KEYBOARD OPERATIONS
Manual Input
The following describes the procedures for manually
entering data into the display buffer (from the keyboard)
for transfer to the I/O channel during a Specific Poll or
General Poll operation:
1. Position the cursor in the character position where the
message is to begin. Refer to Tables I and 2 to select
a keyboard keyes) that will facilitate positioning the
cursor.
2. Depress the SHIFT key and simultaneously depress
the START key. This causes the SaM symbol to be
entered in the display buffer and to appear on the 2265
screen in the character position previously occupied
by the cursor. The cursor is advanced to the next display
position.
3. Key in the message to be transferred to the I/O channel.
The message data will appear on the 2265 screen as the
character keys are operated. The cursor symbol auto-
matically advances as data is displayed on the 2265
screen.
4. After the entire message is displayed on the 2265 screen
and is Visually verified, depress the ENTER key. This
causes all the keys on the keyboard except all ERASE
keys, the RESET key, and TEST key to be locked, and
initiates an Enter operation. The ENTER key causes the
2845 to respond to a poll command by sending the
display message to the central processor.
5. Upon successful completion of the poll, the keyboard is
I
restored, the ENTER PENDING indicator is extinguished,
and the SaM symbol is deleted from the screen. These
actions notify the operator that the Enter operation has
concluded with a successful transmission of the message.
Another message may now be entered at the Display
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