SN74HC240DBR

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Logic- Buffers, Drivers, Receivers, Transceivers

A logic buffer, driver, receiver, or transceiver is a type of electronic device that amplifies, isolates, or converts signals between digital and analog interfaces. The SN74HC240DBR is one such device that combines the functions of a buffer and a three-state output driver and is typically used to buffer address and data buses in TTL-to-TTL applications. It has two 8-bit bidirectional ports, A and B, with four control control inputs: Output Enable (OE), Input Enable (IE), Input Enable A (IEA) and Input Enable B (IEB). By controlling the inputs, the device can be used as an analog buffer, a digital buffer, or as a line-driver receiver.

SN74HC240DBR Application Field

The SN74HC240DBR is used primarily in TTL-to-TTL or asynchronous applications. It can be found in computer and telecommunications systems, microprocessors and microcontrollers, data acquisition systems, voltage-to-frequency converters, precision motor control systems, and process control systems. By configuring the device as an analog buffer (with both OE and IE active) it can be used to level-shift logic signals from one logic family to another.

SN74HC240DBR Working Principle

The SN74HC240DBR consists of eight individual, logic-level-sensitive, inverting buffers. Each buffer contains two logic-level-sensitive input gates, a combination of two NAND gates, which provide the logic level sensitivity. The output of the NAND gates is connected to a pair of D flip-flops, which latch the data. The data can be changed by changing the logic level of the input gates.

The buffer has four control inputs that can be used to enable or disable the device. The Output Enable (OE) signal when low enables the device, while a high logic level on OE will disable the device. The inputs, Input Enable (IE), Input Enable A (IEA) and Input Enable B (IEB) are all active-low, meaning that a low logic level enables the device, while a high logic level disables the device.

When all the control inputs are low, the SN74HC240DBR acts as a buffer, meaning that the input signal applied to A is amplified and appears at the output B, while the input signal applied to B is inverted and appears at the output A. If IEB is high and IEA is low, the function of the device reverses, meaning that the input signal applied to A is inverted and appears at output B, while the signal applied to B is amplified and appears at output A.

When OE is high, the output drivers are disabled and the device appears to be in the high-impedance state. This means that the outputs assume a high-impedance state ignoring any input signals from A and B, and any data previously stored in the flip-flops will be retained. When OE is low, the outputs assume the data present in either A or B, depending upon the states of IEA and IEB.

The SN74HC240DBR is a versatile device that can be used to buffer and drive data buses, level shift, and provide bus isolation and isolation between logic families. By configuring the device as an analog buffer (with both OE and IE active) it can be used to level shift logic signals from one logic family to another. The low-power CMOS process makes the SN74HC240DBR ideal for use in low-power applications.

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