The hardware of early Cinematronics and Vectorbeam CPUs implemented an instruction, Jump on External High (JEH). JEH branched if an input from the game's soundboard (connected to J4-10 on the CCPU) was logic level HIGH. This instruction was used only once, for reading the joystick in Tailgunner. Later boards replaced this instruction with a more useful one: Jump on Minus (JMI) which branches when the result of the preceeding calulation is negative.
Later boards include a jumper that can be removed to allow the use of JEH and disabiling the JMI instruction.
I have searched the code of all the Vectorbeam and Cinematronics games for use of JMI and JEH. Below are the results of this search:
These games can run on a board without JMI: (Confirmed on Tailgunner Hardware)
Space War / Space Wars (no JMI or JEH instructions)
Speed Freak (no JMI or JEH instructions)
All others require JMI to be installed to run:
Rip Off (JMI)
Star Castle (JMI)
Armor Attack (JMI)
Solar Quest (JMI)
Boxing Bugs (JMI)