DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Dynamic random access memory arrays are generally described in U.
S.
Pat.
No.
4,081,701, issued to White, et al.
and assigned to Texas instruments Incorporated.
High density monolithic semiconductor memory devices constructed with multiple arrays formed thereon are well known in the art.
See, for example, U.
S.
Pat.
No.
4,636,986 to Pinkham, also assigned to Texas Instruments Incorporated and incorporated herein by reference, which illustrates a dual port, i.
e.
, both random and serial access, memory device such as provided for video RAM applications.
Normally, each of the multiple arrays comprises an equal number of active memory elements arranged in rows and columns.
Strings of address data are provided to common row and column decoders of the multiple arrays to simultaneously access a memory cell in each array.
Separate input/output buffers are associated with each array for parallel transfer of data, either stored or to be stored in the arrays, to and from an external source.
It has been proposed that the input to individual arrays on such a device can be controlled to selectively write data to less than all the memory cells having a common address.
To this extent, the U.
S.
Pat.
No.
4,636,986 to Pinkham discloses a write mask circuit for inhibiting data transfer to addressed memory locations and also teaches formation of a bit mapped video display memory device wherein writing of data into each of several arrays on the device is controllable with a separate Column Address Strobe signal CAS.
In the past the concept of restricting data input to less than all memory cells having a common address has been largely, if not solely, applied to dual port memory designed into graphic display systems because unique advantages are manifest when writing graphics data or providing enhanced graphics capabilities.
Moreover, while devices which include the write mask feature have become commercially popular, it is not known that video RAM designs which incorporate multiple Column Address Strobe control lines have generated any significant commercial interest
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