AM3270/TR3271 Reference Manual

Details of the CRT Protocol
AM3270 Subdevice Protocols
4–10 086705 Tandem Computers Incorporated
Message Format—
Outbound Data
Figure 4-3 shows the format for outbound CRT messages.
Figure 4-3. CRT Protocol Message Format—Outbound Data
014
C
M
D
W
C
C
Screen Orders
Write Count
Passed by the Application
S
T
X
E
S
C
C
M
D
W
C
C
E
T
X
B
C
C
Screen Orders
Sent to the
Terminal Controller
For outbound data, AM3270 expects the buffer to contain only the textual part of a
screen (from the command character (CMD) through the end of the screen orders and
the text). As illustrated in Figure 4-3, AM3270 adds an STX ESC at the beginning of
the buffer and an ETX after the last character, followed by a BCC.
Message Format—Inbound
Data
For inbound data, the buffer passed back to the application contains the complete data
message starting with the Attention ID (AID) character, as it was received from the
subdevice. Communication characters and the terminal identification address are
deleted. Although a 3271 terminal controller can send input data in up to 256-byte
pieces, AM3270 passes a single buffer back to the application.