A transaction processing system includes a payment reader for processing payment transactions. The payment reader receives payment information from a payment interface. The payment information is processed based on firmware instructions that are stored in memory and executed by a processor. A first subset of the firmware instructions is associated with transaction processing modules. Each of the transaction processing modules comprise position independent code and are located in a distinct section of memory from a second subset of firmware instructions and the position independent code associated with each of the other of the transaction processing modules.