  We present a compact all-digital implementation of a scanning transfer cavity
lock (STCL) for long-term laser frequency stabilization. An interrupt-driven
state machine is employed to realize the STCL, with the capability to correct
for frequency drifts in the slave laser frequency due to measured changes in
the lab environmental conditions. We demonstrate an accuracy of 0.9 MHz for
master laser and slave laser wavelengths of 556 nm and 798 nm as an example.
The slave laser is also demonstrated to dynamically scan over a wide frequency
range while retaining its lock, allowing us to accurately interrogate atomic
transitions.
