Product number (marketing number) 6ES7521-1BH10-0AA0 Product description SIMATIC S7-1500, digital input module, 16 digital inputs x 24 V DC bus coupler, 16 channels in groups of 16, input delay typ. 3.2 ms, input type 3 (IEC 61131); scope of delivery includes front connector push-in Product Family SM 521 Digital Input Modules