Siemens 6ES7421-7BH00-0AB0 Industrial Automation Module — Legacy Replacement. Siemens 6ES7421-7BH00-0AB0 is the exact manufacturer order number for a industrial automation module in the SIMATIC S7-400 portfolio. Siemens describes this exact reference as: SIMATIC S7-400, DIG.INPUT MOD. SM 421, OPTIC. ISOLATED, 16 DI, 24V DC WITH 0,1 MS INPUT DELAY, ALARM, DIAGNOSTICS. The verified manufacturer lifecycle record is PM500:Discontinued Product or end of PLM & Support.