Siemens 6ES7421-1BL00-0AA0 ,Simatic S7-400,SM421; DI 32xDC24V Siemens 6ES7421-1BL00-0AA0 Simatic S7-400, SM 421 32 Channel Digital Input Module 24V DC Mfr. Part Number: 6ES7421-1BL00-0AA0 Manufacturer: Siemens Siemens 6ES7421-1BL00-0AA0 SIMATIC S7-400 SM421 Digital Input, 32-P, Sink, 24VDC Siemens have a few different series under the Simatic name, the 6ES7421-1BL00-0AA0 is from their S7-400 range which is the most powerful of all the Simatic controllers. This PLC is most likely to be found in industries where short machine cycle time and high processing speeds are most necessary, such as manufacturing and process automation. Siemens released the Simatic S7 family in 1995, almost 40 years after their first Simatic controller, and today it is still one of the most popular PLC solutions around. With the S7, users can program their PLC with Siemens STEP 7 software, which will be a breeze particularly for people with experience of the previous STEP 5 program. Users of the S7-400 will know that it is 'hot swappable' which means that you can add or remove modules whilst the controller is live, making it so much easier to add or remove modules.