Programmable timer module coupled to microprocessor system

Abstract

A programmable timer module (PTM) is provided as a component of a microprocessor system in order to generate and measure varying time intervals under program control. The programmable timer module includes, in one embodiment, three independent 16-bit timers. Each timer includes a 16-bit counter and a 16-bit latch. The programmable timer module also includes an 8-bit status register and an 8-bit control register each of which may be coupled to an 8-bit bidirectional data bus of a microprocessor system. Selection circuitry is provided which permits the microprocessor to select either the control register or the status register. Information can be written into the control register; the operation is effected by means of read/write circuitry and a read/write input. Any one of the three timers can also be selected by means of the selection circuitry, and a 16-bit number can be written into the selected 16-bit latch. Reset circuitry resets the counter whenever the 16-bit latch is written into, and the counter counts until it reaches the number written into the 16-bit latch, whereupon the interrupt circuitry generates an interrupt signal and sets an appropriate interrupt bit in the status register, and also resets that counter. The counter continues counting at the appropriate clock rate after the interrupt so that time since the interrupt may be determined by the microprocessor. The outputs of the three counters can be selected as outputs of the programmable timer module.