SWITCH STATE DETECTOR AND ENCODER
A switch state detector for use in a system wherein a plurality of n switches (S 1, . . . , Sn) produces on a single line ( 22 ) a number of discrete voltage levels each representative of one particular state of open and closed switches. The switch state detector comprises a plurality of reference voltage sources each of which corresponds to one of the discrete voltage levels and a set of comparators (C 1, . . . , Cm- 1 ) each having a first input connected to the single line ( 22 ) and a second input connected to one of the reference voltage sources. The switch state detector further comprises a decoder ( 24 ) with inputs receiving the outputs from the comparators (C 1, . . . , Cm- 1 ) and with outputs ( 28 ) providing a digital representation of the particular state of each of the switches (S 1, . . . , Sn). There is further provided an encoder comprising a plurality of n switches (S 1, . . . , Sn) and encoding circuitry interconnecting said n switches, as well as a method for communicating an information representative of a particular state of a plurality of n open and closed switches on a single line ( 22 ).
1 . A switch state detector for use in a system wherein a plurality of n switches produces on a single line a number of discrete voltage levels, each representative of one particular state of open and closed switches, the switch state detector comprising:
a plurality of reference voltage sources each of which corresponds to one of said discrete voltage levels;
a set of comparators each having a first input connected to said single line and a second input connected to a respective one of said reference voltage sources; and
a decoder with inputs respectively receiving the outputs from said comparators and with outputs providing a digital representation of the particular state of each of said switches.
2 . A switch state detector according to claim 1 , wherein said plurality of n switches produces on said single line m discrete voltage levels, with m=2 n .
3 . A switch state detector according to claim 2 , wherein said set of comparators comprises m-1 comparators.
4 . A switch state detector according to claim 1 , wherein said decoder has n outputs, each output corresponding to one of said n switches.
5 . A switch state detector according to claim 1 , wherein said decoder has a further input receiving a strobe signal and provides said digital representation of the particular state of each of said switches upon reception of said strobe signal, the strobe signal further controlling a switch to connect the single line momentarily to a voltage source through a fixed resistor.
6 . A switch state detector according to claim 1 , wherein the switches are analog switches.
7 . An encoder comprising a set of n switches and encoding circuitry interconnecting said n switches and producing on a single line a number of discrete voltage levels each representative of one particular state of the open and closed switches.
8 . An encoder according to claim 7 , wherein said plurality of n switches produces on said single line m discrete voltage levels, with m=2 n .
9 . An encoder according to claim 7 , wherein the encoding circuitry comprises a plurality of diodes, the anode of each diode being connected to the single line and the cathode of each diode being connected to a respective one of the switches.
10 . An encoder according to claim 7 , wherein the switches are analog switches.
11 . A method for communicating information representative of a particular state of a plurality of n open and closed switches, the method comprising:
encoding the state of the n switches into a discrete voltage value representative of said particular state of the n open and closed switches;
transmitting the discrete voltage value on a single line;
comparing the transmitted discrete voltage value representative of one particular state of the n open and closed switches to discrete reference voltage values each corresponding to one possible state of open and closed switches; and
using the results of the comparing step to provide n digital output signals, each representative of the state of a respective one of the n switches.