Siemens 6ES7421-5EH00-0AA0 Digital Input Module — Legacy Replacement. Siemens 6ES7421-5EH00-0AA0 is the exact manufacturer order number for a digital input module in the SIMATIC S7-400 portfolio. Siemens describes this exact reference as: SIMATIC S7-400, DIGITAL INPUT SM 421, OPTIC. ISOLATED, 16 DI, 120 V AC, WITH 1 COMMON POINT. The verified manufacturer lifecycle record is PM500:Discontinued Product or end of PLM & Support.