VMS Help Sys Parameters, TTY_SILOTIME  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    TTY_SILOTIME defines the interval at which the DMF32 hardware
    polls the input silo for received characters. The DMF32
    asynchronous terminal controller can delay the generation
    of a single input interrupt until multiple characters have
    accumulated in the input silo. TTY_SILOTIME specifies the number
    of milliseconds that the characters are allowed to accumulate
    prior to the generation of an input interrupt by the hardware.