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C.1
RS-485 Supports Auto Flow Control
ARK-3440 COM1 port connector located on the rear panel and COM4 can be config-
ured to operate in RS-232, RS-422 or RS-485 mode by adjusting the "Onboard Serial
port 3 Mode" & "Onboard Serial port 4 Mode" of "Integrated Peripherals" in the BIOS.
Refer to Chapter 3 "BIOS Operation" for details on changing this setting. The default
setting for both COM1 and COM4 is RS-232.
C.1.1
Flow Control, Introduction
Consider the situation where someone is helping you harvest fruit from a tree. Your
helper climbs up the tree and throws the fruit down to you. You have to put them in
buckets. In the normal situation, you can easily catch the fruit, but when one bucket is
full and it has to be replaced by an empty one, this action takes more time than is
available between two fruit thrown by your helper.
Two different things can occur. Your helper stops until the new bucket is in position,
or some fruit are damaged because they fall on the (rock hard, as it happens) ground
in the small period you are not able to catch them.
You would probably prefer the first method where your helper stops for a short time.
To achieve this, there will be some communication, eye-contact, a yell, or something
like that to stop him/her from throwing new fruit. How simple, but is it always this sim-
ple? Consider the situation where one computer device sends information to another
using a serial connection. Now and then, the receiver needs to do some other
actions, to write the contents of its buffers to disk for example. In this period of time
no new information can be received. Some communication back to the sender is
needed to stop the flow of bytes on the line. A method must be present to tell the
sender to pause. To do this, both software and hardware protocols have been
defined.
ARK-3440 User Manual
Figure C.1 BIOS COM port setting
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