  The ISIS buncher system at TRIUMF operates at frequencies of 23MHz, 46MHz,
and 4.6MHz. The 23MHz and 46MHz signals drive two buncher cavities, while the
4.6MHz signal drives the 5:1 selector. The previous analog-digital hybrid
system has been replaced with a new digital LLRF system due to occasional
drifts in the setpoints of the control loops during operation. The reference
signal for the LLRF system is obtained from the pickup signal of the
cyclotron's cavity, ensuring that all frequencies are synchronized with it. In
the event of a spark occurring in the cyclotron's cavity, the LLRF system may
lose its reference signal. To address this, a phase-locked loop with a track
and hold function is designed to maintain the frequency when the reference
signal is absent. The 4.6MHz frequency is derived by dividing the 23MHz
reference signal frequency by 5. Designing the divide-by-5 circuitry posed
specific challenges in a binary system. The LLRF system is built upon TRIUMF's
versatile digital LLRF hardware system, with firmware optimized specifically
for the ISIS buncher system. This paper will delve into the details of the
hardware and firmware.
