Texas Instruments RFM003B User Manual

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If you are going to operate more than one TIRIS reader in a local area, the systems
should be synchronized to each other. An intelligent control unit achieves this syn-
chronization by sampling for the presence or absence of the field strength indicator
signal RXSS-. A power pulse in the area will cause RXSS- to be active. If the signal
RXSS- is present the control unit ensures that the RF module transmits either simul-
taneously or sequentially to any other RFMs in the area.

The RXSS- output switches to “low” if the received signal strength exceeds the inter-
nal reference level. This reference level can be adjusted with the two receiver signal
strength control inputs RSCA and RSCB. 

Figure 12 and Figure 13 show the basic schematic of the signal strength indicator
and two methods of adjusting the switching level. 

The circuit shown in Figure 12 works as a simple D/A converter where the digital in-
puts RSCA and RSCB are switched either to the ground GNDL or to the supply volt-
age VSRL. Because of the high input impedance of RSCA and RSCB, the switches
can be replaced by computer controlled outputs. Such a circuit can adjust the sensi-
tivities in four steps. A fifth step is given if both inputs are open.