INS8253 Datasheet | National Semiconductor

Description The INS8253 is a programmable timer/counter device contained in a standard, 24-pin dual-in-line package. The chip, which is fabricated using N-channel silicon gate technology, provides counting or time-out services in a microputer system. The various operating modes and other functional characteristics of thel NS8253 are programmed by the system software. The INS8253 provides three independent 16-bit down counters, each of which is capable of count rates in the range DC to 2MHz. Through software initialization, each counter can be made to operate in anyone of six modes. The modulus and counting system used are also specified by system software. The operating characteristics of any individual counter can be modified by the software at any time to meet changing system requirements. The modulus of any given counter can be changed at the program's discretion by loading a new value into the counter. A counter load operation may be limited to the counter's least significant byte or to its most significant byte, or it may revise both halves of the counter. Count sequences may be in either binary or BCD. This choice is also individually specified for each counter by the software. The contents of each counter may be read either directly or through an auxiliary register. A direct reading of the counter can be made whenever the counter is inhibited from counting. A count value can also be read without interfering with the counting process. This is done by transferring the counter's current value to an auxiliary register and then reading that register. This counter-to-register transfer can be executed without affecting the normal count sequence. Features - 3 Individually Programmable 16-Bit Counters - 6 Operating Modes - DC to 2MHz Count Rates - Individual Count Rate and Modulus for Each Counter - Selectable Counting System (Binary or BCD) for Each Counter - TRI-STATE@ TTL Drive Capability for Bidirectional Data Bus - Single + 5 Volt Power Supply - 24-Pin...