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Write Operation
The process of sending a write-type command and executing that command is called
a write operation. The 3708 supports four write commands:
• Write
\V'I)
• Erase/Write (EW)
• Erase/Write Alternate (EW A)
• Erase All Unprotected (EAU).
The W, EW, and EWA commands are used by the application program to load,
format, and erase selectively areas of the device buffer within the 3708. These
commands can also initiate certain display operations, such as copying the contents
of the display screen, restoring the keyboard, and sounding an audible alarm at the
display. In the data stream, they are normally followed by the Write Control
Character Byte.
The Write Control Character (WCC) Byte
The Write Control Character
\V'ICC)
is not a unique code, but is identified by
position. That is, it is the byte following the write-type command. If the WCC is
omitted, whatever follows the write-type command is interpreted as the WCC. The
data stream is normally a W, EW, or EWA command followed by the WCC,
followed by any orders or data (see "Orders and Attributes" on page 4-10 for
information about orders).
If
any write command (except EAU) is sent with no
WCC or data, it is treated as a no operation.
The following table shows the format of the WCC byte. The printout format bits
are ignored for LU type 2; they are used only for LU type 3. When orders or data
follow the WCC, the 3708 performs the reset of the MDT before processing the rest
of the data. After the processing is complete, all other WCC functions are
performed.
Bit
Meaning
0,1
These bits are determined by bits 2 - 7 according to the control
character I/O codes as described in Appendix E.
2,3
00
=
Let NL, EM, and CR orders in the data determine line length.
(Effectively provides a 132 character line length.)
01
=
40 character print line
10
=
64 character print line
11
=
80 character print line
4
When set to 1, start printing after write completed.
5
Sound alarm if device supports one.
6
Restore operation of the keyboard from input inhibited state.
7
Reset all MDT bits in device buffer before writing or executing orders.
Chapter 4. Protocol Conversion Mode
4-5
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