Manual

5-4 RS-232C Communications
If the System becomes Paused, it simply stops extracting characters from the input buffer.
Eventually the buffer fills up and, if all goes well, the handshake prevents the host from
sending more characters. When the Paused state is cleared, the System resumes processing
the characters. As soon as the buffer becomes empty enough, the handshake allows the host
to resume transmission.
Escape Sequences
Escape sequences are used to establish communications parameters. They are processed
immediately; they are not placed in the input buffer and are not inhibited by the Paused state.
(For an exception to this rule, see the ES command in Chapter 3.) See Chapter 6 Escape
Sequences.
The names of the escape sequences are here represented as
ESC.X which stands for three
ASCII characters: Escape (character code 27), followed by Period (character code 46),
followed by a specified third character.
The host application software and driver software must coordinate their use of escape
sequences to provide for smooth and reliable system startup, to properly respond to error
conditions, and to avoid output conflicts. An output conflict occurs when an escape
sequence requests output before the last character of a previous output request has been
transmitted. (The previous request could be either an ACL command or an escape
sequence.) See the
ESC.E command in Chapter 6.
Hardwired DTR Handshake
The Hardwired DTR (Data Terminal Ready) handshake works as follows. The host
establishes a Block Size; characters are always sent to the Automove System in groups
smaller or equal to the Block Size. If the Automove System has room for a block of
characters in the buffer, it sets the Data Terminal Ready, CD, line to the High state
("asserted"). When there is insufficient room for a block, the System sets Data Terminal
Ready to the Low state ("deasserted"). The DTR signal is electrically connected to the host;
the host should not transmit any characters (or should not begin a new block of characters)
while the DTR line is Low.
The Hardwired DTR handshake is enabled at power up or by using the
ESC.@ command.
The Block Size is established via the
ESC.H or ESC.I command; it defaults to 80, which is
long enough for most typical PRINT statements. Note that the Hardwired DTR handshake
can be active simultaneously with the Xon/Xoff or Enq/Ack handshake.