74HCT245 Octal Bus Transceiver IC DIP-20 – TTL-Compatible, 3-State, Bidirectional

74HCT245 Octal Bus Transceiver IC – DIP-20, TTL-Compatible, 3-State

The 74HCT245 is an octal (8-bit) bidirectional bus transceiver with TTL-compatible inputs and 3-state outputs – the TTL-input version of the popular 74HC245. The key difference: the 74HCT245 accepts TTL logic levels (VIH = 2.0V) at its inputs, making it the correct choice for interfacing 5V TTL logic with CMOS systems, or for level shifting between 3.3V and 5V systems when the driving side uses TTL thresholds. Eight bidirectional buffers with direction control (DIR) and output enable (̅O̅E̅) in a single DIP-20 package.

Electrical Specifications

• Part Number: 74HCT245 / SN74HCT245N / MC74HCT245AN
• Package: DIP-20 (through-hole, 2.54mm pitch)
• Channels: 8 (bidirectional)
• Supply Voltage: 4.5V – 5.5V (5V operation)
• Input Thresholds: TTL (VIH = 2.0V, VIL = 0.8V)
• Output Drive Current: ±25mA per pin
• Propagation Delay: ~10ns (typical at 4.5V)
• Direction Control (DIR): HIGH = A→B, LOW = B→A
• Output Enable (̅O̅E̅): Active LOW – pull HIGH to tri-state all outputs
• Operating Temperature: −40°C to +125°C

74HCT245 vs 74HC245 – When to Use Each

• 74HC245: CMOS inputs (VIH = 0.7×VCC) – use when driving from CMOS logic (Arduino, ESP32)
• 74HCT245: TTL inputs (VIH = 2.0V) – use when driving from 5V TTL logic or for 3.3V↔5V level shifting
• Both have identical output specifications and pinout
• Use 74HCT245 when the input signal may not reach 0.7×VCC (e.g., 3.3V signal driving a 5V 74HC245)

Typical Applications

• Data bus buffering: Bidirectional 8-bit data bus isolation and buffering
• 3.3V ↔ 5V level shifting: Interface 3.3V microcontrollers with 5V peripherals
• Bus isolation: Separate bus segments with tri-state control
• TTL to CMOS interface: Buffer 5V TTL signals for CMOS systems
• Memory interface: Data bus buffering for SRAM and EEPROM

Package Contents

• 1 × 74HCT245 DIP-20 octal bus transceiver IC

Eight bidirectional TTL-compatible buffers with 3-state outputs – the 74HCT245 is the correct choice for 5V TTL bus buffering and 3.3V↔5V level shifting in digital systems.

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