FX707 Code Selector

The FX707 is a PMOS monolithic 3-way 5-pole logic switch intended for use with the CML FX407/507/607 5-tone sequential code transceivers. It allows any one of three programmed codes to be selected by applying logic levels to two control pins. The required codes are programmed by linking each of the three sets of five output pins to appropriate digits at the FX407/507/607 tone select inputs, using wire links, thumbwheel switches or other selector means.
In addition to the code select switching, the FX707 contains circuits which recognize codes containing identical consecutive digits and automatically select the repeat tone frequency (R) at correct points in the code sequence. This exclusive feature permits direct decimal ’as written' programming of code numbers and eliminates errors and difficulties which identical digits cause in manually and automatically variable encoding systems. An on-chip strobe generator rejects noise inputs caused by wiring interaction when coding switches are located at a distance from the decoder.
Combining the FX707 with an FX407/507/607 transceiver provides a complete 5-tone selective call system capable of vehicle to vehicle, talk through, status transponding and other advanced operating modes with major savings in cost, size and engineering complexity compared with alternative conventional methods. Only one external component is necessary for correct operation of the FX707. C_R(to ground) must be connected to the R output. The value of C_R must exceed 250x the maximum possible capacitive loading that might occur on any other output pin. In most systems a value of C_R=0.47µF will be sufficient.