a programmable hold mode which will allow the timer 60 to operate in a very low current mode thus saving battery life this feature is an important consideration in a long duration timer especially to minimize overall costs a winbond w741 series microcontroller is suggested as suitable for this use but any microcontroller having the requisite number of i o ports its own programmable timer and a hold or other low power operational mode could be used firmware that controls microcontroller 64 of timer 60 is attached at appendix a a fourteen pin lead edge connector 62 provides all of the i o needed to interface the timer 60 with a personal computer pc to program the timer 60 seven i o lines are used to store data into the microcontroller ports ra 0 ra 2 are control flags and ports rb 0 rb 3 are actual data transfer lines data is entered into the microcontroller 64 in 4 bit packs the ready line is used to signal the pc that the microcontroller 62 us ready to accept data the remaining lines are or can be used for diagnostics this interface can also be used to read back programmed data to the programming pc for quality assurance the interface can be exposed on the exterior of the inner.