EM4022V20WS11 datasheet(7/15 Pages) EMMICRO

7 / 15 page

 2002, EM Microelectronic-Marin SA

www.emmicroelectronic.com

EM4022

MUTE and WAKE-UP timing diagrams

Fig. 7

WAKE-UP

An ACK sent after correct reception of a code is

interpreted by the other transponders in the field as a

WAKE-UP.

The ACK arrives synchronously at the

transponder

that

has

just

transmitted,

but

asynchronously at all the other transponders. If

necessary, a WAKE-UP can also be sent if the code is

not received correctly, ensuring that it will not be

interpreted as an ACK by the transmitting transponder.

This could speed up the protocol, but runs the risk of

turning transponders off by accident.

To detect a WAKE-UP, the chip checks for two GAPs,

less than 7 bits apart and each less than seven bits

wide. As with the MUTE allowance must made for the

spread in clock frequencies. To be safely interpreted as

a WAKE-UP, the GAPs should be sent less than 5 bits

apart, and each should be less than 5 bits wide.

This has an implication in the case of the high frequency

ACK, which could theoretically consist of two very narrow

GAPs 6 bits apart. In practice though, the GAPs will be

typically at least one bit wide, making the separation five

bits.

Like the MUTE, the low frequency ACK GAPs should be

at least 1.5 bits wide to serve as a reliable WAKE-UP.

It should be noted that failure to reliably recognise

WAKE-UPs is not critical. The protocol might be slowed

down marginally, but will still work, as the chips time-out

of the sleep mode automatically after 128 bits.

EM4022V20WS11 Datasheet(PDF) 7 Page - EM Microelectronic - MARIN SA