AM3270/TR3271 Reference Manual

Details of the PRT Protocol
AM3270 Subdevice Protocols
4–18 086705 Tandem Computers Incorporated
Message Format Figure 4-5 shows the PRT protocol message format.
Figure 4-5. PRT Protocol Message Format
016
Text Line to be Written
Write Count
Passed by the Application
S
T
X
E
S
C
C
M
D
W
C
C
E
M
E
T
X
Text Line to be Written
Printer Orders
Added by AM3270
B
C
C
The printer protocol takes an output buffer containing pure text and adds the
appropriate 3270 printer orders to it. The buffer is then written to the subdevice. A
printer subdevice is a WRITE only device and rejects any READ requests issued to it.
As illustrated in Figure 4-5, AM3270 adds an STX, an ESC, a command (in this case,
the 3270 command, ERASE/WRITE), and a WCC (a 3270 write control command) at
the beginning of the buffer. The protocol appends an EM (a 3270 printer order, end of
message) and an ETX after the last text byte.
Applicable File-System
Procedures
For AM3270/PRT protocol, the following file-system procedures are recognized:
AWAITIO DEVICEINFO
CANCEL FILEINFO
CLOSE OPEN
CONTROL WRITE
Note that all file-system procedures are documented in the System Procedure Calls
Reference Manual. File system procedures CONTROL 1 and WRITE have special
significance for this protocol and are also discussed in this section.