Channel data buffer apparatus for a digital data processing system

Abstract

Channel data buffer apparatus for buffering data being transferred between an input/output channel unit and a main storage unit in a digital data processing system. In the disclosed embodiment, data is generally transferred between the channel unit and the data buffer (a 'channel/buffer' transfer) in two-byte segments and between the main storage unit and the data buffer (a 'storage/buffer' transfer) in eight-byte segments. The data buffer is comprised of eight column-forming byte-wide multirow storage arrays each having its own address mechanism for accessing any desired row therein. Corresponding rows in the different storage arrays provide the corresponding eight-byte rows for the data buffer as a whole. For storage/buffer transfers, data buffer address circuitry is provided for enabling a group of eight contiguous bytes to be read out of or written into the data buffer on a single access even though some of the bytes may be located on one row of the data buffer and other of the bytes on the next row of the data buffer. For channel/buffer transfers, data buffer address circuitry is provided for enabling a group of two contiguous bytes to be read out of or written into the data buffer on a single access even though one of the bytes may be located on one row of the data buffer and the other of the bytes on the next row of the data buffer. For storage/buffer transfers, an eight-byte wrap-around data shifter is located between the data buffer and the main storage unit for enabling any necessary alignment or realignment of the data being transferred. These features enable data to be loaded into the data buffer in a packed manner and without regard to the storage word boundary alignments in the main storage unit. Among other things, this minimizes the hardware needed for buffering the data and improves the data chaining capability of the system.