6ES7288-1ST40-0AA0 is the DC/DC/DC CPU ST40 in the SIMATIC S7-200 SMART controller family. It combines processor memory, 40 onboard digital channels and the principal communication interfaces in a 125 mm-wide housing.

The article provides 24 inputs for 24 V DC signals and 16 transistor outputs for 24 V DC loads. Program development and maintenance use STEP 7 Micro/WIN SMART.

• Executes compact machine logic with 24 KB of program memory and 16 KB of user-data memory.
• Connects local sensors and actuators directly through the integrated 24-input and 16-output channel set.
• Provides Ethernet/PROFINET and RS485 connectivity for programming, controller communication and supported field devices.
• Accepts an optional microSDHC card for the supported transfer and maintenance workflows.
• Handles time-critical control with 150 ns bit execution and the integrated high-speed counter and pulse-output resources.

• Install the CPU on the supported DIN rail with clear access to the removable terminal blocks and communication ports.
• Use a regulated 24 V DC source within the specified operating range and separate signal wiring from high-energy conductors.
• Map the 24 input and 16 transistor-output terminals against the cabinet drawings before reconnecting field devices.
• Apply the temperature limit for the actual mounting orientation: horizontal and vertical installations have different upper limits.
• Confirm the Micro/WIN SMART project, communication addresses and any memory-card procedure before CPU replacement.

• This AA0 article is listed for spare-part use within the S7-200 SMART family.
• Keep the complete 6ES7288-1ST40-0AA0 number because later revisions may differ in environmental or certification details.
• Archive the program, communication settings and expansion-module order before removing the installed CPU.
• A replacement review should compare onboard I/O count, output technology, firmware and network configuration as one set.