Hi,
SBs 250 and 251 are intended for the Standard Series Vision controllers, so they will not accomplish what you're looking to do.
On more recent controllers those system bits have had their function replaced by the "Legal Entry" Link on almost all on-screen elements you'll use.
Previously, the standard series controllers did not have that "Legal Entry" link, so SB 250 and 251 were required.
SB 2 will only be high for a single pulse on power-up. SB 2 is perfect for running one-time configuration/initialization whenever the controller is turned on.