How to Differentiate：74HC595 vs. 74LS595 vs. 74HC164 vs. MCP23017[FAQ&Video]

74HC595 Overview

The 74HC595 is a silicon gate C2MOS high-speed CMOS 8-BIT SHIFT REGISTERS/OUTPUT LATCHES (3-STATE) integrated circuit. An 8-bit serial-in, parallel-out shift register feeds an 8-bit D-type store register in this device. There are 8 3-STATE outputs on the storage register. Both the shift register and the storage register have their own clocks.

For cascading, the shift register includes a direct-overriding clear, serial input, and serial output (standard) pins. Positive-edge triggered clocks are used in both the shift register and the storage register. The shift register state will always be one clock pulse ahead of the storage register if both clocks are coupled together. Static discharge and transient excess voltage safety circuits are installed on all inputs.

74LS595 Overview

An 8-bit serial-in, parallel-out shift register feeds an 8-bit D-type storage register in the 74LS595. The outputs of the storage register are either parallel 3-state ('LS595) or open-collector ('LS596). Both the shift register and the storage register have their own clocks. For cascading, the shift register features a direct-overriding clear, serial input, and serial output pins.

The clocks in the shift register and storage register are both triggered on the positive edge. The shift register state will always be one clock pulse ahead of the storage register if the user decides to connect both clocks.

74HC595 vs.74LS595

74HC595 vs.74LS595

• The 74LS595 is a TTL-based device that is quick, consumes more power, and is older.

• The 74HC595 is a CMOS-based device that is fast, consumes less power, and is the most recent iteration.

• To be more specific, the LS series is based on TTL (total transistor logic) and is made with bipolar transistors (BJT). BJT transistors were among the first to appear in integrated circuits.

• The HC series uses CMOS (complementary metal-oxide-semiconductor) devices, which are a type of later-generation transistor in which the gate is made of metal rather than oxide (now polysilicon over an oxide).

• The input impedance of these devices is much higher than that of a BJT, resulting in significantly lower current and power consumption.

• In general (with exceptions), CMOS is utilized in low-power logic devices, while BJTs are employed in higher-power logic devices (switching, power management apps, etc). There are also BiCMOS devices, which combine CMOS and BJTs on the same die and take advantage of each device's finest features.

74HC164 Overview

The 74HC164 is a serial-in/parallel-out shift register with an 8-bit resolution.

There are two serial data inputs (DSA and DSB) and eight parallel data outputs on the device (Q0 to Q7). Data is entered serially by DSA or DSB, with either input serving as an active HIGH enable for data entry via the other. On the clock (CP) input's LOW-to-HIGH transitions, data is moved. A LOW on the master reset input (MR) clears the register and causes all outputs to be LOW, regardless of the state of the other inputs. Clamp diodes are used as inputs. This allows current limiting resistors to be used to interface inputs to voltages greater than VCC.

Like the CD4015, the 74HC164 has serial in and parallel out, but the 74HC595 is faster and has a lower voltage.

74HC595 vs.74HC164

74HC595 vs. 74HC164

The 74HC164 differs from the 74HC595 in that it does not buffer the data (internal space was present on the 74HC595), therefore the LED FLASHES as it pulls the bits to the tip-toe, producing the flashing effect observed on the 74HC164 but not on the 74HC595.

To be more detailed:

• The output of the 74HC595 has a latch, so it can remain unchanged during the shift; the output of the 74HC164 does not have a latch, so it changes every time a shift clock is created. This is the most significant distinction between the two.

• To achieve a multi-chip cascade, the 74HC595 utilizes a specific Q7 pin; the 74HC164 cascades directly using output pin Q7.

• When the enable OE is faulty, the output pin of the 74HC595 is a high impedance, but the 74HC164 has no enable pin.

• The shift register is reset by the 74HC595. If you want to reset the LATCH register, you must load the contents of the shift register into the latch register on the rising edge of ST CP; that is to say, the 74HC595 reset is synchronous, but the 74HC164 reset is asynchronous.

• The parallel-to-serial chip 74HC165 corresponds to the 74HC164.

MCP23017 Overview

The MCP23017 is a port expander that provides nearly similar PORTS to conventional microcontrollers such as Arduino or PIC devices, as well as interrupts. It uses an I2C interface to provide an extra 16 I/O pins as well as extensive interrupt control.

74HC595 vs. MCP23017

74HC595 vs. MCP23017

In a nutshell, the 74HC595 is a shift register and the MCP23017 is an IO Expander.

• If you just want to drive LEDs directly, the 74HC595 is a decent choice, but if you want something more flexible in your projects, the MCP23017 is a solid option, and they can both run on the same software.

• The key differences between a shift register and an IO Expander are the speed and complexity of driving them.

• Shift registers are simpler serial to parallel converters that are easier to drive. Shift registers will run as quickly as you can feed them data.

• IO expanders are more adaptable, although they are restricted to the i2c interface, which is quite sluggish. SPI expanders would be preferable, although they are still slower than shift registers. There are advantages and disadvantages to everything, and in most circumstances, you can use either one; yet, individuals prefer to utilize the one with which they are most familiar.

74HC595 Datasheet

74LS595 Datasheet

74HC164 Datasheet

MCP23017 Datasheet