7400 Series Guide: 74HC245/74LS245 (Octal Bus Transceiver)

The 74×245 (ex 74HC245) is a chip designed as an octal bus transceiver with 3-state outputs, allowing for bidirectional data transmission between different parts of a digital system.

In this guide, you’ll learn the things you need to know about this chip in order to use bus transceivers effectively in your own projects.

What does the 74HC245 / 74LS245 do?

The 74×245 is a bidirectional bus transceiver. It helps data flow between two separate buses, enabling communication in both directions. The chip has 8 data lines that connect each bus on either side of the chip.

You’ll control the direction of data flow with a direction (DIR) input. When DIR is HIGH, data moves from bus A to bus B, and when DIR is LOW, data travels from bus B to bus A.

There is also an output enable (OE) input. When OE is LOW, the transceiver works to transfer data. If OE is HIGH, the buses are disconnected, causing both sides to be in a high-impedance state. This high-impedance state helps prevent interference with other devices on the same bus.

The 74×245 is useful when you need to manage data flow and prevent conflicts in systems like microprocessors and memory circuits.

How To Use This Chip

The 74HC245 comes in a 20-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC245 supports 2V to 6V, while the 74LS245 only supports 5V.

74HC chips can normally supply a maximum of 4 mA from an output pin. If you’re using the 74LS version, the maximum current you can pull out of one output pin is 0.4 mA when the pin is high (sourcing) or 8 mA when the pin is low (sinking).

But these values can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use the Bus transceiver inside.

74×245 Pinout

The 74×245 has 20 pins and contains Enable and direction pins control output enables laid out as shown in the pinout diagram below:

Pin Name	Pin #	Type	Description
DIR	1	Input	Direction control input. Determines data flow direction: A to B when high, B to A when low.
A1	2	Input/Output	Data bus line A1.
A2	3	Input/Output	Data bus line A2.
A3	4	Input/Output	Data bus line A3.
A4	5	Input/Output	Data bus line A4.
A5	6	Input/Output	Data bus line A5.
A6	7	Input/Output	Data bus line A6.
A7	8	Input/Output	Data bus line A7.
A8	9	Input/Output	Data bus line A8.
GND	10	Power	Connect to ground (GND).
B8	11	Input/Output	Data bus line B8.
B7	12	Input/Output	Data bus line B7.
B6	13	Input/Output	Data bus line B6.
B5	14	Input/Output	Data bus line B5.
B4	15	Input/Output	Data bus line B4.
B3	16	Input/Output	Data bus line B3.
B2	17	Input/Output	Data bus line B2.
B1	18	Input/Output	Data bus line B1.
EN	19	Input	Output enable input (active low). Enables the transceivers when low.
VCC	20	Power	Positive power supply. Connect to +5V power.

Alternatives and Equivalents for 74HC245 / 74LS245

There are many versions of the 74×245 chip. They all have the same functionality, but with different specifications such as supported voltages and maximum current output.

Here’s a list of a few equivalents of this chip:

• 74HC245 (High-speed CMOS)
• 74HCT245 (High-speed CMOS, TTL compatible)
• 74LS245 (High-speed TTL)
• 74LVC245 (Low Voltage TTL)
• 74AC245 (Advanced CMOS)
• 74ALS245 (Advanced Low-Power Schottky TTL)
• 74F245 (Very High Speed)
• 74C245 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC245 and SN74LS245 by Texas Instruments.

Can’t find the 74×245 anywhere? Then try one of the following IC alternatives:

• 74×240 – Octal buffer/line driver with inverting outputs.
• 74×241 – Octal buffer/line driver with non-inverting outputs.
• 74×244 – Octal buffer/line driver with non-inverting outputs.
• 74×540 – Octal buffer/line driver with inverting outputs.
• 74×541 – Octal buffer/line driver with non-inverting outputs.
• CD4503 – Hex non-inverting buffer with 3-state outputs.

If you can’t find the 74×245 IC in your local electronics store, don’t worry, you’ll most likely find it in one of the stores listed on this page of online stores where you’ll find components and tools for all your electronics projects.

Datasheet for the 74LS245 and 74HC245 chips

Download the PDF datasheet for your version of the 74×245 here:

• SN74HC245 (Texas Instruments)
• SN74LS245 (Texas Instruments)
• 74HC245 (Futurlec)
• 74LS245 (Futurlec)
• 74HC245 (Nexperia)