Alstom GEM80-500 Series, Техническое руководство

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4. Serial Communications GEM80-500 Series Controller
GEM80-500 Technical Manual (T2025En) (08/04) Page 4-4
4.4.2 Terminal Mode
This mode is specifically intended for interactive operator interfacing using a VDU and
keyboard terminal or VDU terminal. It performs the functions of auto-echoing and line
editing without the need for user programming.
The terminal is expected to have the following characteristics (ASCII character names
are shown in parentheses):
(1) Pressing the carriage-return key generates @0D (CR).
(2) Pressing the Delete/Rub out key generates @7F (DEL).
(3) Receipt of @0D, @0A (CR, LF) moves the cursor to the left-hand edge of
the screen on the next line, scrolling the display if on the last line of the
screen.
(4) Receipt of @00 (NUL) performs no action.
(5) Receipt of @07 (BEL) sounds an audible alarm.
(6) Receipt of @08 (BS) moves the cursor one character position to the left.
(7) Receipt of @20 (SP) blanks out the current display position.
(8) Receipt of @1A (SUB) displays a non-blank character.
As for direct mode, the port has an input cyclic buffer and an output cyclic buffer. Data
can be written to the output buffer, and read from the input buffer, by means of GEM
80 Special Functions. This is the only way to access these buffers from the GEM 80
Ladder Diagram User Program.
However, the input channel has a separate input line buffer in addition to the input
cyclic buffer. All received characters are initially stored in the line buffer. They are only
transferred to the input cyclic buffer when a @0D (CR) is received and, until this
happens, cannot be read by the controller.
As characters are received into the line buffer, they are echoed back to the VDU via the
output channel and are displayed on the VDU screen, with the following exceptions:
1. Any non-printing character other than CR, DEL, XON or XOFF is
discarded (not loaded into the line buffer) and echoed as BEL
.
2. XOFF is discarded, and causes output (including echoing) to be
suspended.
3. XON is discarded, and causes output suspended by XOFF to
resume.
4. DEL is discarded, and causes the previous character loaded into
the line buffer to be removed. It is normally echoed as BS, SP,
BS. However, if the line buffer is already empty, BEL is echoed.
5. CR is echoed as CR, LF, plus the user-defined quantity of NUL
characters. It is stored in the line buffer as an end-of-line
marker (@0A). Once this has been done, the contents of the line
buffer are transferred to the input cyclic buffer and the line buffer
is then cleared
6. Any character other than CR which would cause the line buffer to