74HCT240

The 74HCT240 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HCT240 is 4-bit parallel load registers with clock enable control, 3-state buffered outputs (Q₀ to Q₃) and master reset (MR).

When the two data enable inputs (E₁ and E₂) of the 74HCT240 are LOW, the data on the Dn inputs is loaded into the registersynchronously with the LOW-to-HIGH clock (CP) transition. When one or both E_n inputs are HIGH one set-up time prior to the LOW-to-HIGH clock transition, the register will retain the previous data. Data inputs and clock enable inputs are fully edge-triggered and must be stable only one set-up time prior to the LOW-to-HIGH clock transition.

The master reset input (MR) of the 74HCT240 is an active HIGH asynchronous input. When MR is HIGH, all four flip-flops are reset (cleared) independently of any other input condition. The 3-state output buffers are controlled by a 2-input NOR gate. When both output enable inputs (OE₁ and OE₂) are LOW, the data in the egister is presented to the Qn outputs. When one or both OE_n inputs of the 74HCT240 are HIGH, the outputs are forced to a high impedance OFF-state. The 3-state output buffers are completely independent of the register operation; the OEn transition does not affect the clock and reset operations.