DESCRIPTION
The SMJ44C251B/MT42C4256 multiport video RAM is a high-speed, dual-ported memory device. It consists of a dynamic random-access memory (DRAM) organized as 262144 words of 4 bits each interfaced to a serial-data register or serial access memory (SAM) organized as 512 words of 4 bits each

FEATURES
• Class B High-Reliability Processing
• DRAM: 262144 Words × 4 Bits
    SAM: 512 Words × 4 Bits
• Single 5-V Power Supply (±10% Tolerance)
• Dual Port Accessibility–Simultaneous and Asynchronous Access
    From the DRAM and SAM Ports
• Bidirectional-Data-Transfer Function Between the DRAM and the
    Serial-Data Register
• 4 × 4 Block-Write Feature for Fast Area Fill Operations; As Many
    as Four Memory Address Locations Written per Cycle From an
    On-Chip Color Register
• Write-Per-Bit Feature for Selective Write to Each RAM I/O; Two
    Write-Per-Bit Modes to Simplify System Design
• Enhanced Page-Mode Operation for Faster Access
• CAS-Before-RAS (CBR) and Hidden Refresh Modes
• All Inputs/Outputs and Clocks Are TTL Compatible
• Long Refresh Period: Every 8 ms (Max)
• Up to 33-MHz Uninterrupted Serial-Data Streams
• 3-State Serial I/Os Allow Easy Multiplexing of Video-Data
    Streams
• 512 Selectable Serial-Register Starting
• Split Serial-Data Register for Simplified Real-Time Register Reload