1. A method of reprogramming a field device in a process control network having a plurality of devices which are communicatively linked on a bus and which use a standard communication protocol to perform process control functions, the method comprising the steps of: downloading program instructions from a host device over the bus to one of the field devices having a storage device having a first memory portion with stored program instructions and a second memory portion using the standard communication protocol during operation of the process control network while the one of the field devices is enabled to execute the stored program instructions that will be replaced by the downloaded program instructions to perform process control; storing the downloaded program instructions in the second memory portion of the storage device while the one of the field devices is enabled to execute the stored program instructions that will be replaced by the downloaded program instructions to perform process control, wherein the one of the field devices alternately receives and stores the downloaded program instructions and executes the stored program instructions to perform process control until the downloaded program instructions are fully downloaded and stored in the second memory portion; and causing the field device to discontinue executing the stored program instructions to perform process control and to execute the downloaded program instructions to perform process control.