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DISPLAY SCREEN
Field Attributes
Field attributes control how data in that field will be
displayed on the display screen. They control display
blinking, intensity, underscoring, column separation,
reverse image, and no display. The application program
controls field attributes. After power on, field attributes
will default to normal intensity, no blinking, no
underscoring, no column separators, and no reverse
image when the screen is refreshed. Field attributes
occupy one character space position and it is the first
character of the field.
Display Screen Indicators
These indicators appear on the display screen. A bright
square indicates the on condition and a dash indicates
the off condition. The controller controls the indicators,
except the System Available indicator. Power-on resets
all indicators.
The display screen indicators, when on, indicate the
following:
• System Available - indicates that the display station
has received a poll or a command. This indicator will
turn off if the display station does not receive a poll
or command for 200 ms.
• Message Waiting - indicates that a message is
waiting for the operator.
• Keyboard Shift - indicates that the display station is
in upper (numeric) keyboard shift.
• Insert Mode - indicates that the key has started an
operation.
• Input Inhibited - indicates that the system cannot
process a keyboard scan code.
A cursor, controlled by the M PU or controller, indicates
a position on the display surface, usually where the next
keyboard character will be displayed.
CABLE ADAPTER
The cable adapter is the hardware (drivers, receivers,
and logic) on the planar board that handles the incoming
and outgoing communications between the controller
and the display station.
Note: A twinaxial cable connects the display station to
the controller. See the Customer Twinaxial Cable section
in the maintenance section of this manual, and the
Cable Thru description in the Features section.
The 16-Bit Frame
Frame Concept
Communications between the controller and the cable
adapter at the display station are carried by 16-bit
frames that are sent to and from the controller on an
as-required basis. The cable carries no signal between
frames.
To understand what is to follow, it is necessary to
explain briefly the phase encoding used for sending data
on the system cable. The data is phase encoded so that
a transition occurs during each bit time (a 0 to 1
transition for a 0 and a 1 to 0 transition for a 1).
Because the transition divides the bit into 2 parts, the
term half bit will be used in the explanation that fol-
lows. (The data sent on the system cable is a 4 level
signal. Refer to the system documentation for a fur-
ther explanation of the phase encoding process.)
When information is to be sent on the cable, a group of
five 1 bits (1010101010 half bits) is sent to establish bit
synchronization. Immediately after the 1 bits, a group of
3 half bit 1's and 3 half bit O's is sent to establish frame
synchronization. After the frame synchronization half
bits, the frame is sent, starting with the sync bit.
The transmission rate is 1.0 MHz (16 microseconds
per frame). The frame bit assignment during transmit
and receive is shown in the following diagram:
Theory
5251 MIM
4-9
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