The Emerson VersaMax Micro 28 is a powerful and versatile micro PLC designed for a wide range of small to mid-scale automation applications. Part of the PACSystems family, this controller combines the flexibility of a modular design with a compact footprint, making it an ideal choice for machine builders and system integrators who need reliable performance in limited panel space.

Modular Design and I/O Expandability

The VersaMax Micro 28 features a robust modular architecture that provides exceptional flexibility. The base unit includes 28 built-in I/O points, configured as 16 discrete inputs and 12 discrete outputs. For applications requiring additional capacity, the system can be expanded with a wide range of VersaMax expansion modules, supporting up to 140 I/O points (some configurations up to 170 points). This scalability allows the controller to grow with application needs without requiring a complete hardware replacement.

Performance and Memory

At its core, the Micro 28 delivers fast and deterministic control with a scan time of just 1.1 milliseconds per 1K instructions. This ensures rapid response for time-critical processes. The controller is equipped with 9 KB of user logic memory and 2 KB of data memory, providing ample space for application code and data storage. For more demanding applications, the VersaMax Micro family supports up to 128 KB of total memory on higher-end models, offering a clear migration path.

Communication and Programming

Connectivity is a key strength of the Micro 28. It features two built-in serial ports: an RJ-45 RS-232 port and a DB-15 RS-485 port. These ports support multiple protocols, including SNP Slave, Modbus RTU Slave, and serial I/O commands, enabling seamless integration with HMIs, SCADA systems, and field devices. An optional second port can be configured for RS-232, RS-485, USB, or Ethernet connectivity. Programming is intuitive with Emerson's PAC Machine Edition software (formerly Proficy Machine Edition), which supports relay ladder diagram and instruction list programming in a unified development environment. The controller also supports online programming changes and a portable flash memory module for field upgrades without a PC.

Motion Control and High-Speed I/O

For applications requiring precise motion control, the VersaMax Micro 28 includes built-in high-speed counter functionality, supporting Type A and Type B configurations. It also provides two independent 65kHz pulse and direction outputs, making it suitable for basic stepper and servo motor control. These integrated motion capabilities eliminate the need for separate motion modules in many applications, reducing system cost and complexity.

Applications

The Emerson VersaMax Micro 28 is ideally suited for a variety of industrial automation applications, including:

• Small to mid-scale machine control and packaging machinery
• HVAC systems and building automation
• Material handling and conveyor systems
• Plastic injection molding and auxiliary equipment
• Pump control and water/wastewater treatment
• Basic motion control and positioning tasks

Technical Specifications

Parameter	Value
Manufacturer	Emerson
Series	VersaMax Micro
Product Type	Micro PLC
Built-in I/O Points	28 (16 inputs, 12 outputs)
Max Expandable I/O	140 points (up to 170 on some configurations)
Scan Time	1.1 ms / 1K instructions
User Logic Memory	9 KB
Data Memory	2 KB
Built-in Serial Ports	2 (1 x RS-232 RJ-45, 1 x RS-485 DB-15)
Optional Second Port	RS-232 / RS-485 / USB / Ethernet
High-Speed Counter	Built-in (Type A / Type B)
Pulse Output	2 channels, 65kHz pulse/direction
Programming Software	PAC Machine Edition / VersaPro
Operating Temperature	0 °C to 55 °C (horizontal)
Protection Degree	IP20
Mounting	DIN rail or panel mount
Certifications	CE, UL, cUL, RoHS