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circuitry can latch the receiver on until all data is received;if no carrier is detected

it can immediately be put back to “sleep”.

By pulsing the receiver on/off, the

average supply current may often be reduced by a factor of 20 or more,

depending upon the system requirements. The data detect output is valid within

3ms after application of the supply.

DATA CODING

Once a reliable RF link has been established, the challenge becomes how to

most effectively transfer data across it. Since the transmit and receive modules

have no internal digital coding/decoding, a user has tremendous flexibility to

send many types of analog and digital data. It is important to understand,

however, that some intelligent transmission structure must be used.This is true

for several reasons. The first and most significant is that there must be some way

to distinguish an intended transmission from interferers and ambient noise. In

addition, it is generally not possible to hold DC levels across an RF link;

therefore, transitions must take place at minimum intervals. The designer must

always structure his protocol to take into account such considerations in order to

assure a reliable and error-free wireless link. For further information on such

issues you may wish to refer to the application note section of the Linx internet

site @www.linxtechnologies.com.

Application-specific data encoding and transfer is often accomplished using a

microprocessor. Inexpensive micros such as the Microchip PIC series make an

excellent choice for this task.They can directly interface to the RM’s data output.

If you do not have a microprocessor on-board your product and you want to send

control signals such as a key press, switch closing, or low-rate data, consider

using an encoder and decoder IC chipset.These chips take care of all encoding,

error checking, and decoding functions and are available from a number of

manufacturers including Linx.An example of such an application is shown on the

following page.

Figure 9: Simple circuit implementing carrier detect