Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual page 81

• Status Bit 1, Character Request - Character request
means that the Transmitter Holding register is empty
and a new character can be accepted. Loading jata
into it drops the character-request condition ~ntil
the register is again empty.
• Status Bit 2, Character Ready - Character ready
means that the Receiver Holding register has a char-
acter in it that can be removed by the processor.
If the character is not removed within a character
time, the following character received is trans-
ferred into the holding register, thus destroying
the character {lost data}.
The character ready status is dropped by executing a
read data function.
• Status Bit 3, Receive Error - The receive error con-
dition can be generated by:
Parity Error - The Parity bit received in the
character does not match the one generated by the
receiver.
Framing Error - No Stop bit was detected in the
Stop bit slot of the character.
Lost Data - A new character was received and
transferred into the Receiver Holding register
before the processor removed the previous one.
The Status bit does not indicate which of the possi-
ble causes actually forced the error condition.
Software should be prepared to recover from this
mode of failure {request retransmission}. The error
condition is cleared automatically by reception of a
new character containing no errors, provided that
the character-ready condition does not exist when
this happens.
• Status Bit 4, Serial Channel Carrier Detected - This
bit, active low, indicates that the data set Carrier
Detect signal is active at the serial channel
interface.
• Status Bit 5, Clear to Send - This bit indicates
that the data set Clear to Send signal is active.
• Status Bit 6, Data Set Ready - This bit indicates
that the data set connected to this interface is
ready.
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