Siemens 6ES5900-7AC21 CPU Module | 16-Bit

This Siemens CPU module serves as the primary processor for S5 automation systems. The Siemens 6ES5900-7AC21 executes control programs with high efficiency and reliability. Its powerful architecture handles both logic and arithmetic operations effectively. This module supports system expansion with additional I/O modules.

Physical Dimensions and Mounting Details

The module measures 232 mm in height and 25 mm in width. Its overall depth reaches 160 mm including the front connector. This unit weighs approximately 0.6 kilograms for stable rack installation. The housing features a robust metal casing for electromagnetic shielding. The Siemens 6ES5900-7AC21 plugs directly into any S5 rack slot. A 48-pin backplane connector transfers power and signals.

Processor and Memory Architecture

A 16-bit microprocessor with 10 MHz clock speed handles all computational tasks. This processor executes bit operations in 0.3 microseconds for rapid response. Word operations complete in 1.5 microseconds for efficient data handling. The unit includes 32 KB of RAM for user program and data storage. A separate 64 KB EPROM holds the operating system firmware. The Siemens 6ES5900-7AC21 provides 16 KB of retentive memory for critical data. An integrated lithium battery maintains this memory for up to 5 years. An internal capacitor of 680 µF bridges brief power interruptions.

Communication and System Capabilities

This CPU offers one RS-232 port for programming device connection. A second RS-485 interface supports remote I/O and inter-controller communication. The unit handles up to 512 digital I/O points for system flexibility. It also manages up to 64 analog channels for process monitoring. The Siemens 6ES5900-7AC21 processes 1024 instructions in approximately 2.5 milliseconds. Four interrupt inputs enable priority-based event handling. A watchdog timer monitors program execution continuously.

Detailed Specification Table

Parameter	Specification
Dimensions (H x W x D)	232 mm x 25 mm x 160 mm
Weight	Approx. 0.6 kg
Processor Type	16-bit microprocessor
Clock Frequency	10 MHz
Bit Operation Time	0.3 µs
Word Operation Time	1.5 µs
RAM Capacity	32 KB
EPROM Capacity	64 KB
Retentive Memory	16 KB
Battery Backup Life	5 years
Energy Storage Capacitance	680 µF
Digital I/O Capacity	512 points
Analog Channel Capacity	64 channels
Program Execution Time	2.5 ms / 1024 instructions
Communication Ports	RS-232, RS-485
Interrupt Inputs	4

Application and Commissioning Guidelines

Insert this CPU into the designated slot of the S5 rack system. Connect the programming device to the RS-232 port for initial setup. Download the user program and system parameters via the serial interface. The Siemens 6ES5900-7AC21 operates reliably between 0°C and 60°C. Ensure sufficient airflow around the CPU for proper heat dissipation. Configure the communication settings to match peripheral device requirements. Monitor the front-panel LEDs for system status and fault indicators. Replace the backup battery every four years to prevent memory loss.