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HP 27130B
Three options are available to indicate that a backspace has occurred when the card is in echoplex
mode. The first option is "backspace echo". This option echoes a backslash character (SC hex), fol-
lowed by the character that was deleted from the input buffer.
The second option is "backspace overwrite". This option is very useful for CRT-type terminals. The
firmware will echo a backspace - space - backspace sequence for each BACK SPACE key hit, erasing
the character from the screen.
The third option is "backspace only". This option echoes only the backspace character to move the cur-
sor under the deleted character.
The Backspace option is programmable by using WCC, SF 8. Only one backspace option may be en-
abled at any time.
If you have used backspace to delete the current line, any further backspace will cause no action.
Line Deletion. The firmware uses the character DEL (hex 7F) as the line deletion character. As with
the backspace character, you can program the line deletion character by using the WCC, SF 7.
The line deletion character causes the card to delete the current line, if any. If the card is in echoplex
mode, it will write one backs lash, then do a carriage-return/linefeed to indicate that the buffer was
deleted.
Software Handshake with the Device
Three software handshakes are available between the host and the device:
1. Host controlled ENQ/ ACK handshake
2.
Device controlled X -ON/X-OFF handshake
3. Host controlled X -ON/X -OFF handshake
Besides enabling the individual software handshake defined above by using the WCC, SF 9, you also
must enable the Software Handshake option in WCC, SF 1. Handshakes may be toggled on or off for
the duration of the request by setting the "toggle handshake" bit in the Read Device Data request (RQ
1)
subfunction field. The handshakes will revert to the previous definition when the request com-
pletes. The characters defined for the ENQ, ACK, X -ON, and X -OFF characters are programmable
by using the WCC, SF 22, SF 23, and SF 24.
The following discussion will assume the default characters defined below.
Handshake
Character
ENQ
ACK
X-ON
X-OFF
Default ASCII
Character
ENQ
ACK
DC1
DC3
Hex
Value
05
06
11
13
4-6
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