Siemens 6ES7321-7BH00-0AB0 Digital Input Module — Legacy Replacement. Siemens 6ES7321-7BH00-0AB0 is the exact manufacturer order number for a digital input module in the SIMATIC S7-300 portfolio. Siemens describes this exact reference as: SIMATIC S7-300, DIGITAL INPUT SM 321, OPTICALLY ISOLATED, 16 DI, DC 24V, 20 PIN, PROCESS INTERRUPT, DIAGNOSTICS. The verified manufacturer lifecycle record is PM500:Discontinued Product or end of PLM & Support.