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Commands
Note: The binary number in parentheses next to the
command is the bits 10 through 14 of the command
frame.
Clear (10010):
clears the addressed feature or display
station starting at the present value of the address
counter to the present value of the reference counter.
EOQ
(00010):
designates the end of the command
queue. Bits 8 and 9 of the command frame must be on
(1).
Only polls will be accepted until a not-busy status
is returned to the controller in response to a poll.
Insert Character (00011):
is followed by one data
frame containing a character to be inserted at the
address counter location.
Load Address Counter
(10101):
is followed by two
data words and causes bits 7 through 14 of the data
words to be written in the address counter.
Load Cursor Register
(10111):
is similar to the load
address counter command for the cursor register.
Load Reference Counter
(00111):
is followed by two
data words and loads the reference counter similarly to
the load address counter command.
Move Data
(00110):
moves data between limits set by
the value 'of the address counter and the value of the
cursor register.
Poll (10000):
is sent from the controller to the display
station and starts the transmission of one or two status
words per poll. The poll command acknowledges and
resets a line parity error from the display station. It also
acknowledges the receiving of the last status
transmission by the display station.
Read Activate or Write Activate (Read activate
=
00000;
write activate
=
00001):
is inserted between
a Read or Write command and the data frames that
follow. Either is the command that starts the data
transmission of any of the read or write commands.
, Commands that must be followed by
either a read activate or write activate command.
Read Between Limits' (11010):
causes data to be
returned from an area in read/write storage within the
limits of the address counter register and the reference
counter register.
Read Data'
(01000):
starts the transmission of one
byte of data from the display station to the controller.
Read Registers'
(11100):
starts the transmission of six
data words containing the contents of the three control
registers.
Read to End of Line' (01010):
requests a response
from the display station with one display line of data
from the read / write storage.
Reset
(OOOlO):
resetting can be selected by a specific
address feature or by sending the display station
address for a complete station reset. Attributes are set
to normal, the cursor is moved to the upper left corner.
Search Next Attribute (00100):
causes the·display
station to search the read/write storage for the next
attribute.
Search Next Null (10100):
causes the display station to
search the read/write storage for the next null.
Set Mode (10011):
causes the display station to
receive one word that is specified as a mode control.
This command must be sent before the 5251 makes any
multiframe response.
Write Control Data
(00101):
controls the display screen
during error conditions, conditionally resets the
exception status, controls the keyboard clicker during
input inhibit, and controls the audible alarm.
Write Data and Load Cursor (10001):
is followed by 1
to 14 data frames. The cursor register is updated to the
new value in the address counter.
Write Immediate Data'
(11101):
causes the display
station to store all the data the controller sends. If the
storage area is exceeded, a storage overrun error
occurs.
Theory
5251 MIM
4-11
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