6264

The 6264 is a JEDEC-standard static random-access memory (SRAM) integrated circuit with a capacity of 64 kilobits (8 kilobytes), organized as 8,192 words by 8 bits, designed for high-speed data storage in electronic systems.^[1] It operates on a single 5 V supply and features low-power consumption, including a typical standby current of 10 µW and operational power of around 15 mW at 1 MHz, making it suitable for battery-powered or portable devices.^[2] First introduced in the 1980s by manufacturers such as Hitachi, Motorola, and Samsung, the 6264 has been produced in various access time variants ranging from 70 ns to 200 ns to accommodate different performance needs in applications like embedded systems, game consoles, and early personal computers.^[2] Its static design eliminates the need for external refresh circuitry or timing signals, simplifying integration compared to dynamic RAM alternatives.^[3]

Overview

Description

The 6264 is a JEDEC-standard static random access memory (SRAM) integrated circuit featuring an asynchronous interface, designed for high-speed data access in various electronic systems.^[4] As a volatile memory device, it stores data temporarily during operation but requires continuous power to retain information, offering rapid read and write capabilities without the need for periodic refresh cycles that characterize dynamic RAM (DRAM).^[4] This design makes the 6264 simpler to integrate but more power-intensive compared to DRAM alternatives.^[4] Typically housed in a 28-pin dual in-line package (DIP) with a 0.6-inch width and standard 0.1-inch lead spacing, the chip supports easy mounting on circuit boards via through-hole technology.^[4] Its core purpose is to provide fast, reliable random access storage for temporary data in microcomputers, peripherals, and embedded applications, with a total capacity of 64 Kbit organized as 8K words by 8 bits.^[4]

Capacity and Organization

The 6264 is a static random-access memory (SRAM) integrated circuit with a total capacity of 64 kilobits (Kbit), equivalent to 8 kilobytes (KB) or 65,536 bits. This capacity allows for the storage of up to 8,192 distinct 8-bit words, providing a byte-wide data interface suitable for many early microcomputer designs.^[5][6] Internally, the 6264 is organized as 8,192 words by 8 bits (8K × 8), enabling efficient access to data in byte increments without the need for internal multiplexing common in dynamic RAMs. The organization is fixed as 8K × 8. Data storage relies on a static architecture using bistable latching circuits, which retain information without periodic refreshing as long as power is supplied.^[5][7] Addressing in the 6264 is handled via 13 address input lines (A0 through A12), which directly select one of the 8,192 possible word locations in the memory array. These lines provide a straightforward binary decoding scheme, where the full 13-bit address is applied simultaneously to access the desired 8-bit word, supporting asynchronous operation without clock synchronization. This direct addressing simplifies integration compared to multiplexed schemes, allowing rapid random access within the chip's specified timing parameters.^[5][6] Read and write operations on the 6264 are controlled asynchronously through dedicated signals, including chip enable (CE, often implemented as dual CE1 and CE2 for flexibility in power management) and write enable (WE). For a read cycle, the chip is selected by asserting the appropriate CE signals while holding WE high, placing the selected 8-bit word on the bidirectional data pins (DQ0–DQ7). In write mode, WE is asserted low with valid data and address present, latching the new byte into the addressed location. An additional output enable (OE) signal further refines read access by controlling the data bus state, ensuring high-impedance outputs when deselected to support memory expansion. This signal configuration enables reliable data transfer in bus-oriented systems.^[5][7]

Technical Specifications

Electrical Characteristics

The 6264 SRAM operates on a single supply voltage of 5 V ±10% (V_CC = 4.5 V to 5.5 V), with ground (V_SS) referenced at 0 V. This standard TTL-compatible power requirement ensures compatibility with contemporary digital logic families of the era. Data retention is possible at voltages as low as 2.0 V in CMOS variants, facilitating low-power applications.^[8][5] Access times for the 6264 vary by speed grade, denoted by suffixes such as -70, -85, -100, -120, -150, and up to -200, indicating maximum read or write cycle times from 70 ns to 200 ns. For instance, the -70 variant achieves address access times (t_AA) of 70 ns maximum under typical conditions (V_CC = 5.0 V, T_A = 25°C), while slower grades like the CDM6264CD3 extend to 200 ns for cost-sensitive or low-frequency designs. These timings support cycle times equal to access times in static operation, without the refresh requirements of DRAM.^[8][9][10] Power consumption depends on the operating mode and variant. Active current (I_CC) reaches up to 260 mA maximum in industrial-grade devices during full operation (outputs enabled, cycling at rated speed), though typical values are lower at 30 mA for commercial CMOS versions at 1 MHz. Standby current drops significantly, to as low as 20 mA in TTL standby mode or 15 mA in CMOS power-down (with chip enable high and inputs at extremes) for commercial variants, enabling energy-efficient deselection in multi-chip systems. Note that some manufacturers like Hitachi specify lower CMOS standby currents around 10 µA under specific conditions.^[8][5] The device supports commercial (0°C to 70°C) and industrial (-40°C to 85°C) operating temperature ranges, with specifications guaranteed across these extremes for reliable performance in varied environments. Automotive-grade variants extend similar tolerances.^[8][5] Input and output levels are TTL-compatible, with high-level input threshold (V_IH) at 2.2 V minimum and low-level (V_IL) at 0.8 V maximum; outputs provide V_OH of 2.4 V minimum and V_OL of 0.4 V maximum under standard load conditions (I_OH = -4 mA, I_OL = 8 mA). Three-state outputs ensure bus compatibility when deselected.^[8][5]

Pin Configuration

The 6264 static random-access memory (SRAM) is housed in a 28-pin dual in-line package (DIP), with pins numbered 1 to 14 along one side and 15 to 28 along the opposite side when viewed from the top, where pin 1 is typically identified by a notch, dot, or beveled edge on the package body. This layout facilitates easy insertion into sockets or printed circuit boards, with the pins arranged in two parallel rows spaced 0.1 inches (2.54 mm) apart and the package width measuring 0.6 inches (15.24 mm) for the standard plastic DIP variant.^[5] The core signal assignments include 13 address input pins labeled A0 through A12, which collectively provide the 13-bit addressing required to select one of the 8,192 memory locations (since 2^{13} = 8192). These inputs are TTL-compatible and decoded internally to access the memory array. The eight data pins, D0 through D7 (also denoted as DQ0–DQ7 in some variants), serve dual purposes as bidirectional input/outputs, allowing data to be written to or read from the selected location depending on the control signals; during read operations, they drive output data, while in write mode or when deselected, they act as high-impedance inputs. Control signals consist of chip enable 1 (/CE1, active low), chip enable 2 (CE2, active high), write enable (/WE, active low), and output enable (/OE, active low), which determine the operational mode: for example, asserting /CE1 low and CE2 high selects the device, /WE low enables writing when combined with chip select, and /OE low enables the data outputs during reads. Power and ground are connected to VCC (typically pin 28, +5 V supply) and VSS (typically pin 14, ground), with the device operating over a 4.5–5.5 V range.^[11][5] As a static RAM, the 6264 features a no-refresh design, eliminating the need for dynamic refresh circuitry and thus omitting dedicated clock, row address strobe (RAS), or column address strobe (CAS) pins present in contemporary DRAM chips like the 4164; data retention occurs indefinitely as long as VCC is maintained above the minimum threshold, simplifying system timing but requiring constant power.^[11] Although exact pin numbering can vary slightly by manufacturer (e.g., Hitachi HM6264 vs. Cypress CY6264), a representative pinout for the Hitachi HM6264 series is provided below in tabular form for clarity, based on the standard 600-mil DIP package (top view, pin 1 at upper left). Unused pins (NC) may be tied to ground or left floating per application needs.^[5][11] This configuration supports easy memory expansion in systems by daisy-chaining multiple 6264 chips via shared address and control buses, with chip select signals used for selection.^[5][11]

History and Development

Introduction and Standardization

The 6264 emerged in the mid-1980s as a pivotal advancement in static random-access memory (SRAM) technology, representing the shift from earlier 16 Kbit densities, such as those in the 6116 chip, to 64 Kbit capacities that supported growing computational needs in personal and embedded systems. Datasheets indicate commercial availability starting around 1986.^[12] This expansion addressed limitations in memory scalability for 8-bit architectures, providing a fully static, asynchronous design that eliminated the need for refresh cycles and external timing, thereby improving reliability and speed in battery-backed or high-performance applications. The 6264 adheres to a JEDEC-compatible pinout and electrical interface, ensuring consistent functionality across vendors to promote interoperability and ease of design integration. This standardization facilitated second-sourcing, where multiple semiconductor companies could produce pin-compatible versions without requiring board redesigns, a critical factor in the era's fragmented supply chains.^[13] Initial commercial milestones for the 6264 appeared in datasheets from leading firms starting in 1986, with Integrated Device Technology (IDT) documenting pin-compatible equivalents like the IDT7164 in its high-performance CMOS lineup, followed by Motorola's MCM6264 entries in 1988 memory catalogs. These releases underscored the chip's rapid adoption amid the explosive growth of the personal computer market, where demand for denser, low-power static memory surged to support expanding software and multitasking capabilities in home computers. The 6264's 64 Kbit capacity, typically organized as 8K words by 8 bits, became a staple for such systems.^[12][14]

Manufacturers and Variants

The 6264 static RAM chip was produced by several major semiconductor manufacturers, adhering to JEDEC-compatible standards for interoperability. Primary producers included Hitachi with the HM6264 series, which featured high-speed CMOS designs organized as 8K x 8 bits.^[11] Toshiba offered compatible variants such as the TC5564, while NEC manufactured the μPD6264, both compatible with the standard pinout.^[15] Samsung produced the KM6264, emphasizing low-power operation in its data book specifications.^[16] Other notable manufacturers were Hynix (formerly Hyundai) with the HY6264 and Cypress Semiconductor with the CY6264, ensuring broad availability across the industry.^[17][8] Later, companies like ISSI and Winbond provided drop-in compatible versions such as the AS6C6264 and W2465, maintaining support for legacy systems. Variants of the 6264 were differentiated primarily by speed grades, with access times ranging from 70 ns to 200 ns to suit various performance needs; common designations included -70, -85, -100, -120, -150, and -200, as specified in manufacturer datasheets.^[11] Low-power versions, such as the 6264L series (e.g., HM6264LP), reduced standby current to as low as 10 µW typical, making them ideal for battery-backed applications.^[18] Packaging options encompassed traditional 28-pin DIP for through-hole mounting, as well as surface-mount formats like 300-mil SOP, SOJ, and PLCC to accommodate space-constrained designs.^[5] The JEDEC-compatible pinout ensured cross-compatibility among brands, allowing drop-in replacements without circuit modifications.^[11] Production of original 6264 variants by major manufacturers largely ceased by the early 2000s as they shifted to higher-density memories, though compatible modern versions continue to be manufactured for legacy support, and new old stock remains available from specialized distributors.

Applications

In Microcomputers and Peripherals

The 6264, a 64 kilobit static random-access memory (SRAM) chip organized as 8K × 8 bits, played a significant role in 8-bit microcomputer systems during the 1980s, often serving as working RAM to expand storage capacity beyond the limitations of dynamic RAM (DRAM). In these architectures, it provided reliable data retention without the need for periodic refresh cycles, making it ideal for auxiliary memory in resource-constrained environments, especially when paired with battery backup for persistence across power cycles. Specific implementations highlighted the chip's versatility in peripheral devices. It functioned as buffer memory in disk controllers, where it temporarily stored sector data during read/write operations to ensure data integrity and speed up transfer rates over the system's bus. These buffers mitigated latency issues in mass storage peripherals connected to early PCs like the IBM PC XT. Integrating the 6264 into 8-bit systems presented challenges related to address decoding and bus interfacing, particularly with processors like the Intel 8080 or Zilog Z80. Designers had to implement precise logic for chip select (CS) and write enable (WE) signals to avoid address conflicts, often using additional decoding chips like the 74LS138 to map the 6264 into the system's memory space without overlapping ROM or I/O regions. This required careful PCB layout to manage timing constraints, as the chip's access time of around 150 ns needed to align with the bus cycle of 4-6 MHz clocks typical in these machines. Despite these hurdles, the 6264's advantages shone in real-time operations; its static design eliminated DRAM refresh overhead, enabling consistent performance in peripherals like printer buffers or modem caches, where interruptions could cause data loss or delays. This reliability contributed to its adoption in embedded control systems within microcomputers, enhancing overall system responsiveness.

In Gaming Consoles and Embedded Systems

The 6264 static RAM chip played a notable role in early gaming consoles, where its 8 KB capacity and compatibility with 8-bit systems made it suitable for expanding memory in performance-critical applications. In the Nintendo Entertainment System (NES), the 6264 was integrated into certain mapper chips and expansion modules to provide additional work RAM (WRAM), supporting enhanced sprite handling and temporary data storage during gameplay.^[19] This usage allowed developers to implement more sophisticated features without relying solely on the console's built-in 2 KB RAM. Faster variants, such as those with 70 ns access times, were selected to meet the NES's timing requirements for fluid animation and input response.^[19] Beyond the NES, the 6264 appeared in other console hardware. In Atari 7800 prototypes and cartridge designs, it functioned as work RAM to buffer graphics data and game states, leveraging its pin compatibility with larger RAM types for easy upgrades.^[20] Similarly, in Sega Master System add-ons, hobbyist modifications replaced the system's original DRAM with 6264 SRAM chips to improve reliability and speed in memory expansion kits.^[21] In embedded systems, the 6264's low power dissipation and battery-backup compatibility enabled its use in devices requiring persistent static storage. It was commonly deployed in real-time clocks (RTCs) for timekeeping functions, printer buffers to temporarily hold print data, and industrial controllers for logging operational states without frequent refreshes.^[22] For instance, in pinball machines—an early form of embedded entertainment hardware—the 6264 stored high scores, adjustments, and timestamps, often paired with a battery to maintain data across power cycles.^[22] A key example of the 6264's enduring appeal in gaming is its adoption by the NESdev community for custom cartridges. Enthusiasts incorporate the chip to enable save states and extra memory in homebrew games, allowing players to preserve progress mid-session—a feature absent in original NES hardware—while mimicking authentic 1980s-era constraints.^[19] This approach has facilitated numerous fan projects, demonstrating the chip's versatility in modern retro development.

Legacy and Modern Relevance

Obsolete Status and Replacements

The 6264 SRAM, a 64K x 8 static random-access memory chip introduced in the 1980s, became largely obsolete by the mid-1990s due to the rapid evolution of memory technologies that prioritized higher density and lower power consumption. The shift toward denser dynamic RAM (DRAM) and synchronous DRAM (SDRAM) allowed for greater storage capacities in smaller form factors, rendering discrete 8K-byte SRAM chips like the 6264 inefficient for mainstream applications. Additionally, advancements in CMOS fabrication processes enabled the integration of memory directly into system-on-chip (SoC) designs, diminishing the need for standalone SRAM components in consumer electronics and computing systems. Modern replacements for the 6264 include higher-density SRAM variants such as the 62256 (32K x 8) for expanded capacity needs, as well as integrated memory solutions embedded within microcontrollers and SoCs from manufacturers like Microchip or STMicroelectronics. The Cypress CY6264 series, now produced by Infineon Technologies, provides RoHS-compliant, pin-compatible equivalents suitable for legacy and industrial applications.^[23] For applications needing non-volatility, EEPROM or flash memory modules have supplanted SRAM in scenarios where data persistence without power is essential, providing similar access speeds but with added endurance against power loss. These successors maintain backward compatibility through emulated interfaces in FPGA-based recreations or drop-in equivalents from vendors like Infineon, which produce RoHS-compliant versions for industrial retrofits. In terms of supply chain, original 6264 chips remain available through surplus electronics markets and specialized distributors, but legacy stock often faces challenges with lead-free RoHS compliance, prompting users to seek modern equivalents to meet environmental regulations. Hobbyist communities have developed recreations using contemporary logic families, ensuring functionality in vintage hardware restorations without relying on scarce NOS (new old stock) parts.

Collectibility and Nostalgia

The 6264 SRAM chip holds considerable appeal in retro computing circles for its role in authentic restorations of 1980s-era hardware, including certain Nintendo Entertainment System (NES) cartridges and expansions. Hobbyists prioritize original 6264 chips to maintain the historical integrity of these systems during repairs, avoiding modern substitutes that could alter timing or compatibility. This demand stems from the chip's prevalence in consumer electronics of the period, making it a staple for preserving functional vintage machines.^[19][24] Community-driven preservation efforts have led to extensive online documentation for the 6264, with resources like the NESdev Wiki offering detailed pinout diagrams, compatibility notes, and archived datasheets from manufacturers such as Hitachi. Forums including RetroComputing Stack Exchange and Arcade-Museum provide troubleshooting guides and sourcing advice, enabling collaborative maintenance of systems like arcade cabinets and early PCs that rely on the chip. These platforms ensure that technical knowledge remains accessible, supporting ongoing repairs and educational projects in the retro community.^[19][25][26] Modern recreations of the 6264's functionality cater to vintage enthusiasts through FPGA-based emulations integrated into retro system cores, accurately replicating the chip's 8K x 8 static RAM behavior for projects like NES clones. DIY SRAM modules, often built with microcontrollers such as the Raspberry Pi Pico, further mimic the 6264's interface and timing to facilitate expansions or backups in original hardware without sourcing scarce originals. These approaches blend nostalgia with practicality, allowing hobbyists to extend the life of legacy systems.^[27][28] On the collector's market, new old stock (NOS) 6264 chips command prices ranging from $1 to $10, depending on condition and packaging, with rarer variants from specific manufacturers like Sanyo or Toshiba fetching higher values due to limited availability. Specialty retailers catering to arcade and pinball restorers stock these chips at around $6–$8 each, reflecting steady demand from preservationists.^[29][30]