The SP8855E is one of a family of parallel load synthesisers containing all the elements apart from the loop amplifier to fabricate a PLL synthesis loop. Other devices in the series are the SP8852E which is a fully programmable device requiring two 16 bit words to set the RF and reference counters, and the SP8854E which has hard wired reference counter programming and requires a single bit word to program the RF divider. The SP8855E replaces the existing SP8855D.