The SMJ55166 multiport video RAM is a high-speed, dual-ported memory device. It consists of a dynamic random-access memory (DRAM) module organized as 262 144 words of 16 bits each that are interfaced to a serial-data register (serial-access memory [SAM]) organized as 256 words of 16 bits each. The SMJ55166 supports three basic types of operation: random access to and from the DRAM, serial access from the serial register, and transfer of data from any row in the DRAM to the serial register. Except during transfer operations, the SMJ55166 can be accessed simultaneously and asynchronously from the DRAM and SAM ports. The SMJ55166 is equipped with several features designed to provide higher system-level bandwidth and to simplify design integration on both the DRAM and SAM ports. On the DRAM port, greater pixel draw rates are achieved by the (4 x 4) x 4 block-write feature of the device. The block-write mode allows 16 bits of data (present in an on-chip color-data register) to be written to any combination of four adjacent column-address locations. As many as 64 bits of data can be written to memory during each CAS cycle time. Also on the DRAM port, a write mask or a write-per-bit feature allows masking of any combination of the 16 inputs/outputs on any write cycle. The persistent write-per-bit feature uses a mask register that, once loaded, can be used on subsequent write cycles without reloading. The SMJ55166 also offers byte control, which can be applied in write cycles, block-write cycles, load-write-mask-register cycles, and load-color-register cycles. The SMJ55166 also offers extended-data-output (EDO) mode, which is effective in both the page-mode and standard DRAM cycles.