Timing channel circuitry for controlling stimulation circuitry in an implantable stimulator is disclosed. The timing channel circuitry comprises a addressable memory. Data for the various phases of a desired pulse are stored in the memory using different numbers of words, including a command indicative of the number of words in the phase, a next address for the next phase stored in the memory, and a pulse width or duration of the current phase, control data for the stimulation circuitry, pulse amplitude, and electrode data. The command data is used to address through the words in the current phase via the address bus, which words are sent to a control register for the stimulation circuitry. After the duration of the pulse width for the current phase has passed, the stored next address is used to access the data for the next phase stored in the memory.
