Engine speed sensing device

Claim 1

An engine speed sensing device for use in control of an internal combustion engine having a crankshaft, said engine speed sensing device comprising: a crank angle sensor for producing an angle pulse each time said crankshaft rotates through a predetermined angle; a counter connected to said sensor for counting angle pulses from said sensor; means for determining a time interval during which said counter counts the angle pulses and for producing a control signal when each time interval has elapsed; a leading edge detector for detecting the leading edge of the control signal and for outputting a corresponding detection signal, said detection signal occurring at substantially the same time as said control signal; means responsive to the detection signal for latching the count value of said counter; means for receiving the latched counter value; said latching means comprising a latch element connected between said counter and said receiving means, said latch element being responsive to said detection signal for latching the contents of said counter and for outputting the latched counter contents to said receiving means; said counter being responsive to the control signal to be cleared such that the contents of said counter are latched and then said counter is cleared almost immediately; an interrupt control unit responsive to the detection signal for producing an interrupt request signal, said interrupt control unit comprising a first register, said first register having a bit location which is set to a predetermined state in response to said detection signal; a central processing unit for executing a plurality of different programs; said central processing unit being responsive to the interrupt request signal for reading said first register and being responsive to said predetermined state of said bit location to read the count value latched in said receiving means.