Siemens 6ES7421-1BL01-0AA0 Digital Input Module — Legacy Replacement. Siemens 6ES7421-1BL01-0AA0 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, isolated 32 DI; 24 V DC. The verified manufacturer lifecycle record is PM400:Announcement of product phase-out.