The rewriting device for rewriting data stored in a memory of a vehicle controller
with new data is provided. The rewriting device is capable of communicating with
the vehicle controller. When deleting or writing operation on the memory is not
being performed, the rewriting device determines that communication between the
rewriting device and the vehicle controller is offline if no response from the
vehicle controller within a first determination time. When deleting operation or
writing operation on the memory is being performed, the determination of offline
is prohibited until a second determination time has elapsed. The second determination
time is greater than the first determination time. It is preferable that the second
determination time for deleting operation is the time necessary to delete the data
stored in the memory, and that the second determination time for writing operation
is the time necessary to write the new data into the memory.
