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 process control program instructions from a host device to one of the field devices having a storage device having a first memory portion with stored process control 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 process control program instructions to perform process control; storing the downloaded process control program instructions in the second memory portion of the storage device while the one of the field devices is enabled to execute the stored process control program instructions that will be replaced by the downloaded process control program instructions to perform process control; and causing the field device to discontinue executing the stored process control program instructions to perform process control and to execute the downloaded process control program instructions to perform process control.