Digital timer apparatus and method

摘要

A digital timer apparatus incorporates a free running counter, an interval timer, a capture register, a pulse accumulator; holding logic and mode selection logic. In one mode of operation, a rising or falling edge of an external signal causes the current contents of the free running counter to be loaded into the capture register, causes the previous value of the capture register to be transferred to a holding register and causes the pulse accumulator to be incremented. A read of the capture holding register causes the pulse accumulator value to be transferred to a holding register and causes the pulse accumulator to be reset. The output of the interval timer can cause an interrupt signal to be generated to request service from a central processing unit. The timer apparatus is particularly well suited to performing tasks related to the determination of the speed of rotation of a rotating member and may be used, for instance, in detecting wheel rotational speeds in an anti-lock brake system or detecting shaft rotation speeds in an automatic transmission.