Advantech ARK-3400, User Manual, Page: 78 / 87

ARK-3400 User Manual 66
that the request to send query answers itself. As soon as the RTS output is set, the
CTS input will detect a high logical value indicating that sending of information is
allowed. This implies, that information will always be sent as soon as sending is
requested by a device if no further checking is present. To prevent this from happen-
ing, two other pins on the connector are used, the data set ready DSR and the data
terminal ready DTR. These two lines indicate if the device attached is working prop-
erly and willing to accept data. When these lines are cross-connected (as in most null
modem cables) flow control can be performed using these lines. A DTR output is set,
if that computer accepts incomming characters.
C.1.4 How to implement
Implementing proper flow control can give some headaches. The main problems are
the numerous ways it can be done and especially for null modem connections, the
lack of a standard way of doing. The best way to implement rigid flow control in your
software is to use preprogrammed routines from a reliable source. The problems
involved in the own development of communication routines is often not worth the
effort compared to the relative low prices of professional communication libraries. A
good library is the COMM-DRV/Lib from Willies Computer Software Co. This library
supports all versions of Windows and MS-DOS. XModem, YModem and ZModem file
transfer routines are provided and all source code is included. Includes also Modem
handling and string handling routines.
C.2 WOL Setting
C.2.1 Introduction
Wake on LAN (WOL, sometimes WoL) is an Ethernet computer networking standard
that allows a computer to be turned on or woken up remotely by a network message.
C.2.2 System requirements - PC Compatible
Wake on LAN (WoL) support is implemented on the motherboard of a computer.
Most modern motherboards with an embedded Ethernet controller support WoL with-
out the need for an external cable. Older motherboards must have a WAKEUP-LINK
header onboard and connected to the network card via a special 3-pin cable; how-
ever, systems supporting the PCI 2.2 standard coupled with a PCI 2.2 compliant net-
work adapter typically do not require a WoL cable as the required standby power is
relayed through the PCI bus.
PCI version 2.2 has PME (Power Management Events). What this means is that PCI
cards can send and receive PME via the PCI socket directly, without the need for a
WOL cable.
Laptops powered by the Intel 3945 chipset or newer (with explicit BIOS support)
allow waking up the machine using wireless (802.11 protocol). This is called Wake on
Wireless LAN (WoWLAN).
Wake on LAN must be enabled in the Power Management section of the mother-
board's BIOS. It may also be necessary to configure the computer to reserve power
for the network card when the system is shutdown.
In addition, in order to get WoL to work it is sometimes required to enable this feature
on the card. This can be done in Microsoft Windows from the properties of the net-
work card in the device manager, on the "Power Management" tab. Check "Allow this
device to bring the computer out of standby" and then "Only allow management sta-
tions to bring the computer out of standby" to make sure it does not wake up on all
network activity.