–

–

–

–

10

11

Host Interface Module

The ES Master Development System

features a Host Interface socket, which

allows the use of two different PC interface

modules. The first is a USB interface

module that uses a standard USB cable to

connect to a PC’s USB port or a USB hub.

The second type of module is a RS-232

interface module that can be connected

to a standard serial COM port on a PC

using a straight-through 9-pin extension

cable (not included). The evaluation board

is considered a DCE device and as such

is designed to be connected using a

straight-thru serial extension cable. Do not

use a null-modem cable as the boards will

not function.

To install, select the module to be used

and then line up the pins on the module

with the headers on the board. Verify that the pin one polarity marks on the

board and on the Host Interface Module match. The USB jack or the D-sub

connector should face away from the board. Press firmly on the module so

that it slides fully into the header.

The development system may be prepared

for host operation with the supplied Linx

software by setting the jumpers on the

header as shown in the adjacent figure.

This routes the module’s data lines to

the Host Interface Module. Despite being

electrically interfaced, appropriate protocol

must be employed to ensure reliable and

error-free data transfer since the ES Series

modules do not encode or packetize the

data in any manner. It is important to understand that the development

boards are transparent; that is, the user’s software is entirely responsible

for controlling the timing and error correction aspects of the link. The

evaluation boards have no provision to check or qualify the incoming data.

When designing a protocol to transfer data across a wireless link, it is very

important to remember that interference is inevitable. The protocol must

Figure 7: USB Interface Module

Figure 8: RS-232 Interface Module

TS1

TX

RX

TS2

SQ. DATA

NC

AUDIO REF

AUDIO

RSSI

RX DATA

RX DECODER

RX PDN

PDN ENC

TX PDN

PDN RS232

TX RS232

TX DATA

TX ENCODER

/CLK

/CLK SEL

LO V DET

NC

GND

TS1

TX

RX

TS2

SQ. DATA

NC

AUDIO REF

AUDIO

RSSI

RX DATA

RX DECODER

RX PDN

PDN ENC

TX PDN

PDN RS232

TX RS232

TX DATA

TX ENCODER

/CLK

/CLK SEL

LO V DET

NC

GND

Figure 9: Jumper Configuration

support error detection and correction if it is to be successful. A correctly

designed protocol will provide optimum performance and throughput for

product specific applications while taking into account the timing and

data-rate requirements of the module. For further information on protocol

considerations please refer to Application Note AN-00160.

If the designer needs to develop protocols using a physical implementation

other than an RS-232 or USB interface, the designer can build the custom

interface circuitry in the prototyping area and route the module’s data

signals from the header to the prototyping area.

Master Development Software

The development system is supplied with Windows-based software that

facilitates communication with the development boards through the Host

Interface Module. This software allows for testing and illustrates basic

implementation of the modules as a wireless serial link. The user selects

either a USB or RS-232 connection and whether the connected board is

the transmitter or receiver. The user can then send text, ASCII characters,

and even a picture. Documentation for the software may be found by going

to the ‘Help’ menu then ‘Help File’.

Terminal emulation programs, such as HyperTerminal, do not provide

error correction; therefore, bit errors or data line hashing are displayed as

random characters. Some form of error detection should be employed

when developing a protocol for wireless environments (please see

Application Note AN-00160).

About Antennas

The choice of antennas is one of the most critical and often overlooked

design considerations. The range, performance, and legality of an RF link

are critically dependent upon the type of antenna employed. Linx offers

a variety of antenna styles that can be considered for a design. Included

with the kit is a Linx CW Series connectorized whip antenna that should

be connected prior to using the kit. Despite the fact that the antenna is

not centered on the board’s ground plane, it exhibits a VSWR of <1.7 and

suitably demonstrates the module’s best practical performance.