IBM 2702 Information Manual page 59

IBM TERMINAL CONTROL TYPE II--OPERATIONS
The IBM Terminal Control Type II is designed to
service the IBM 1030 Data Collection System.
Transmission Code
The B CD plus parity code is used between the IBM
2702/03 and the IBM 1030. Figure 2-24 shows an
example of a character in the transmission code.
The start of a character is always signaled by a
start bit (Space level). The end of a character is
always signaled by at least one stop bit (Mark level).
The 2702/03 checks only that there is at least one
stop bit on a receive operation, but when it trans-
mits the 2702/03 sends two stop bits.
The start and stop bits are added to the character
by the terminal control when the 2702/03 is trans-
mitting; these bits are deleted by the terminal con-
trol when the 2702/03 is receiving.
Each received and transmitted character is
checked for odd vertical parity. VR C erros cause
Data Check to be set in the sense register but do not
cause termination of the current command. Unit
Check is also set in the status register.
Transmission Code Converted to Interface Code
Figure 2-25 shows the conversion between the
I/o
interface code and the transmission code. Interface
bits 1-7 are transmitted as B-C bits. Interface
bit position 0 is not used and is always set to 0 for
received data.
VRC (Vertical Redundancy Check)
The IBM Terminal Control Type II checks each
received and transmitted character for odd vertical
parity. VR C errors set the Data Check bit in the
sense byte, but do not terminate the command being
executed.
Special Characters
Figure 2-26 shows the code configuration of the
special characters recognized by the IBM Terminal
Control Type II (IBM TC-II)
Transmit
The following characters are recognized in the IBM
Terminal Control Type II during transmit operations.
@--End of Transmission (EaT). Indicates the end
of transmission and places the IBM TC-II in control
mode.
It
is normally followed by a polling character
or addreSSing character.
@
--End of Address (EOA). Indicates the end of
address (start of text) and sets text-out mode.
Receive
The following characters are recognized by the IBM
TC-ll during receive operations.
@--End of Block (EOB). Indicates the end of a
block of text.
If
a VR C error is detected in the
block of data, the Channel End, Device End, and
Unit Check status is set and the Data Check bit is
set in the sense byte. Normally only the Channel
End and Device End status is set.
@--End of Address (EOA). Indicates that the
following characters will be text and sets text-in
mode.
@
is recognized only
if
the line is in
control mode. Otherwise it has no control effect
and is treated as a normal data character.
®
Received as a Negative Response. A
®
that is
received as a response to addreSSing indicates that
the addressed terminal is not ready to receive data;
Channel End, Device End, and Unit Exception status
is set. A
@
response to polling indicates that the
terminal does not have a message to send; Channel
End, Device End, and Unit Exception status is set.
A
®
reply to text (IBM TC-II text-out mode) indi-
cates a text error and sets Channel End, Device End,
and Unit Check status together with Data Check in the
sense byte. If
@
is received in text (IBM TC-ll in
text-in mode), it is treated as a normal data char-
acter and has no control effect.
G)
Received as a Positive Response to AddreSSing.
Indicates that the addressed terminal is ready to
receive data.
®
received following text (IBM
TC-II in text-out mode) indicates the text was
received without error. In either case, the command
ends with Channel End and Device End status.
If
®
is received while the IBM TC-II is in text-in
mode, it is treated as a normal data character and
has no control effect.
Delete. Delete characters are removed from the
incoming data stream and their transfer to the I/O
channel is inhibited by the IBM TC-II.
Idle. Idle characters are removed from the incoming
data stream and their transfer to the I/O channel is
inhibited by the IBM TC-II.
Operations 2-43