Atari ST series Technical Reference Manual page 42

The speed parameter controls the communications speed,
which is sometimes called the baud rate. The ST XBIOS sup­
ports 16 standard rates of communication, the most common
of which are 300, 1200, 2400, and 9600 bps (bits per second).
The rates represented by the various values of speed are:
Communication speed
Speed Value
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
The handshake parameter is used to indicate which
method of flow control or handshaking is used. Flow control is
used to ensure that the sender isn't sending characters faster
than the receiver can handle them. When the receiver starts
to fall behind, it tells the sender to stop sending characters
until it can catch up. When it catches up, the receiver tells
the sender to start sending again. One method of handshak­
ing is known as XON/XOFF, after the ASCII characters used.
Using this protocol, the receiver sends the XOFF character
(Ctrl-S, ASCII 19) when it wants the other side to stop, and
XON (Ctrl-Q, ASCII 17) when it wants it to start again. The
other major handshaking protocol is known as RTS/CTS.
This method involves the receiver and sender using the RS-
232 hardware lines Ready To Send (RTS) and Clear To Send
(CTS) to indicate when they are ready to send and receive
characters, respectively. The meaning of the various hand­
shake parameters are as follows:
34
CHAPTER 3
(in bits per second)
19200
9600
4800
3600
2400
2000
1800
1200
600
300
200
150
134
110
75
50