1. Field of the Invention
The present invention relates to a data multiplexing apparatus for time-division multiplexing a plurality of kinds of data blocks.
2. Description of the Prior Art
Generally, a conventional time-division data multiplexing apparatus has a circuit arrangement as shown in FIG. 5. This apparatus is shown in "Technology of PCM Communications" by Kaneko, Sanpo Publishing Co., P.11, 1983. The operation of the apparatus will be explained with reference to FIG. 6. As a 4-step rotary switch 7 rotates at a constant speed of one rotation per given period T, first through fourth discrete data blocks are sequentially selected at time intervals of T/4 to form a time-division multiplexed data.
According to such a conventional time-division multiplexing technique, the size of the time slot assigned to each data block is fixed (T/4 in the above case). So, when the data size of each data block is not uniform or varies with time, the rotating period T of the rotary switch must be set so that each time slot can accommodate a data block having a maximum data size. Since such a large time slot is assigned equally to every data block, which has a smaller data size in most cases the amount of unoccupied time will increase. Accordingly, a highly efficient time-division data multiplexing cannot be expected.