Pulse width measurement circuitry

Claim 1

External pulse width measuring circuitry for use in a microprocessor system including a microprocessor unit, a data bus for transferring data between said microprocessor and said measuring circuitry, a control bus for transmitting control signals and system clock signals to said measuring circuitry, an interrupt control circuit for receiving interrupt signals generated external of said microprocessor unit, and a counter circuit, said pulse width measuring circuitry comprising: a control register coupled to the data bus and the control bus for receiving external pulse measurement instruction data from the microprocessor; prescaler and timer control circuitry coupled to said control register and said control bus for generating from said instruction data, the control signals, and the system clock signals, a plurality of output signals for controlling the operation of the pulse width measuring circuitry; a prescaler coupled to said control circuitry and said control bus for generating counting pulses from said system clock signals and at a frequency controlled by said control circuitry, the generation of said counting pulses being enabled or inhibited by said control circuitry output signals representing the leading edge and end-of-pulse transitions, respectively, of said external pulse; and timing circuitry coupled to said prescaler, said control circuitry, said data bus, said control bus, and to the microprocessor interrupt control circuit for counting said counting pulses, storing said count, transferring said count to said data bus upon receipt of a particular first output signal from said control circuitry, and for producing and transmitting to said microprocessor interrupt control circuit an external interrupt request signal upon the occurrence of an end-of-pulse transition of said external pulse.