8.1 Overview

The SN74LV8154 device is a dual 16-bit binary counter with 3-state output registers, designed for 2-V to 5.5-V V_CC operation. The counters have dedicated clock inputs. The counters share a storage register clock and an asynchronous clear input. The 32-bit storage register can be mapped on the output bus 8-bit at a time. Four bus reads are needed to access the contents of both counters. The two counters can be chained by connecting CLKBEN to RCOA

This 16-bit counter (A or B) feeds a 16-bit storage register, and each storage register is further divided into an upper byte and lower byte. The GAL, GAU, GBL, GBU inputs are used to select the byte that needs to be output at Y0−Y7. CLKA is the clock for A counter, and CLKB is the clock for B counter. RCLK is the clock for the A and B storage registers. All three clock signals are positive-edge triggered.

A 32-bit counter can be realized by connecting CLKA and CLKB together and by connecting RCOA to CLKBEN.

To ensure the high-impedance state during power up or power down, GAL, GAU, GBL, and GBU should be tied to V_CC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.

This device is fully specified for partial-power-down applications using I_off. The I_off circuitry disables the outputs, preventing damaging current backflow through the device when it is powered down.