TYPICAL APPLICATIONS (CONT.)
Figure 11 below shows the QS module connected to a microprocessor. This is
the design used in the QS Master Development Kit and the documentation for
the kit describes the connections and software.
SOFTWARE CONSIDERATIONS
The PC needs a set of drivers that tell it how to communicate with the QS module.
There are two types available free from the Linx website. The first are Virtual COM
Port drivers. These drivers make the QS appear as an extra COM port on the host
PC. This allows the application to use standard writes and reads to a serial port, and
the drivers will redirect data to the USB device.
The second set are the Direct Drivers. These drivers support a series of custom
functions that allow more direct control of the QS module. These functions are
described in Application Note AN-00200: SDM-USB-QS-S Programmer’s Guide,
where examples are given in both Visual Basic and C. The Programmer’s Guide can
be downloaded from the Application Notes page in the Support section of the Linx
website at www.linxtechnologies.com. Sample software is available on the Software
page in the Support section.
In addition to the Programmer’s Guide, the QS Master Development System (MDEV-
USB-QS) includes example software and sample system source code. This source
code provides the driver function declarations, examples of how to use the functions
in a program, and other code that may be of use.
Page 11
Page 10
USBDP
USBDM
GND
DSR
DATA_IN
DATA_OUT
RTS
CTS
DTR
TX_IND
VCC
SUSP_IND
RX_IND
485_TX
RI
DCD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
USB Type B
Connector
5V
DAT -
DAT+
GND
1
2
3
4
SDM-USB-QS-S
VCC
RA2/AN2
1
RA3/AN3
2
RA4/AN4
3
MCLR/VPP
4
GND
5
RB0/INT
6
RB1
7
RB2/RX
8
RB3
9
RB4
10
RB5/TX
11
RB6
12
RB7
13
VCC
14
RA6
15
RA7
16
17
RA1/AN1
18
PIC16F88
220
220
220
SW-PB
VCC
200K
VCC
220
220
10K
VCC
220
220
Figure 11: Interface With A Microprocessor
SERIAL NUMBER CONSIDERATIONS
The VID and PID are used by Windows to determine what devices are attached
to the bus and which drivers to load in order to communicate with each device.
A unique serial number is used to distinguish between different devices of the
same type so that the operating system can be sure that it is communicating with
the correct one. Windows will view every different combination of VID, PID, and
serial number as a new device and will start the “Found New Hardware” wizard
for each one. This is an issue in a mass production environment, so the QS
modules are shipped with the “Enable Serial Number” option disabled in the
EEPROM. This prevents the serial number from being used during
ennumeration.
With the serial number disabled, Windows will track each device by connection
and assign a USB port to a particular device. If the device is moved to another
port, it will need to be reinstalled. The problem that arises is that the device will
be installed on the same PC multiple times, once for each USB port into which it
has been plugged.
It is recommended to set the “Enable Serial Number” option and to use a unique
serial number as a part of the final testing procedure of your product. The QS
EEPROM Programmer can be downloaded from the Linx website and the
EEPROM programming functions can be found in Application Note AN-00200.
These can be used as a part of an automated test program at the end of the
production line to program custom descriptors and a unique serial number into
the product.
Avoid using the same serial number for multiple devices, as it can cause a
conflict in the operating system. Windows XP has a particular problem with this
and may crash if it sees two of the same type of device with the same serial
number on the same bus.
HELPFUL APPLICATION NOTES FROM LINX
It is not the intention of this manual to address in depth many of the issues that
should be considered to ensure that the modules function correctly and deliver
the maximum possible performance. As you proceed with your design, you may
wish to obtain the following application notes. They are available on line at
www.linxtechnologies.com or by contacting the Linx literature department.
AN-00200
SDM-USB-QS-S Programmer’s Guide
AN-00201
Installing the SDM-USB-QS-S Drivers
NOTE
APPLICATION NOTE TITLE
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