Dataman S4 - Manual (Page 82)

DATAMAN S4 MANUAL
82 Baud Rates
Baud Rates
The baud-rate of a transmission is the
reciprocal of the time used to send one bit.
Asynchronous serial transmissions as
commonly used by computers have extra bits
to frame and check the data: a START bit, then
the DATA bits, then an optional PARITY bit
and then one or more STOP bits. Baud-rate
indicates the fastest possible transmission
speed: it does not indicate the actual
transmission speed. You can send one byte
per fortnight at any baud-rate. When a
computer has reached its limiting speed for
processing the data, increasing the baud-rate
will not make it send or receive any faster – the
gaps between characters will just get bigger.
Some systems claim high baud rates but they
are slow at receiving data files all the same.
To prevent the sending device supplying data
faster than the receiving device can digest it,
the receiver prompts with a signal RTS
(Request-To-Send), and/or DSR (Data-Set-
Ready). These signals are called handshaking.
Leads used for serial communications must
connect the handshaking signals properly, to
prevent data getting lost. As S4 can actually
receive data-files at 115200 baud with 1 stop
bit, the highest rate supported by a PC, without
stopping the transmission, which means that
there will be no problem even if RTS is not
connected.
S4 has two active handshake signals in each
direction. DTR is provided too and is always
true - it proves only that the cable is connected.