Improved stimulation circuitry for controlling the stimulation delivered by an implantable stimulator is disclosed. The stimulation circuitry includes memory circuitry that stores pulse programs that define pulse shapes, steering programs that define electrode configurations, and aggregate programs that link selected pulse programs with selected steering programs. Each aggregate program is formed from multiple aggregate instructions. The amplitude of pulses defined by an aggregate instruction can be gradually increased to a full value over a specified number of steps and with a specified number of pulses at each step. Different step number and pulses per step can be defined for the first aggregate instruction and succeeding aggregate instructions.
