Microchip Technology 93C66B-I/MS

Overview

93C66B-I/MS from Microchip Technology Inc. is a 4 Kbit, 256 × 16-bit organization serial EEPROM with Microwire-compatible 3-wire interface, operating at 4.5–5.5 V, rated for industrial temperature (−40°C to +85°C), and packaged in an 8-lead MSOP. It features self-timed erase/write cycles, automatic ERAL/WRAL support, and Ready/Busy status signaling via DO pin - used in embedded system configuration storage and calibration data retention.

For engineers reviewing the 93C66B-I/MS datasheet, 93C66B-I/MS pinout, 93C66B-I/MS application, or 93C66B-I/MS equivalent, key selection considerations include its fixed 16-bit word size (no ORG pin), 2 ms program cycle time, 1 million endurance cycles, 200-year data retention, and compatibility with legacy Microwire controllers in space-constrained industrial designs.

Technical Context

The 93C66B-I/MS implements a synchronous serial interface with CS, CLK, and DI/DO pins, requiring no external timing components. Its instruction set includes READ, WRITE, ERASE, ERAL, WRAL, EWEN, and EWDS - all executed via rising-edge clocked bit streams starting with a Start condition (CS high + DI high on CLK edge).

Unlike 'C' variants, the 93C66B has no ORG pin and permanently configures memory as 256 × 16-bit. Write initiation uses the rising edge of CLK on the final data bit (not CS falling edge), and VCC must be ≥4.5 V for ERAL/WRAL operations. Power-on reset circuitry disables writes until EWEN is issued.

Key Specifications

Pinout & Package

8-lead MSOP (Micro Small Outline Package), 3.0 mm × 3.0 mm body, 0.65 mm pitch, exposed pad optional (VSS or floating). Pin 1 marked by laser dot; pin 1 ID corner indicated by chamfer or notch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM applications.

Compared with 93LC66B-I/MS, the 93C66B-I/MS offers tighter V_CC regulation for stable 5 V systems but sacrifices supply flexibility; versus AT25040B-MAU-10, it retains Microwire compatibility and faster WRAL execution but lacks SPI ubiquity and multi-byte page write optimization.

Availability

93C66B-I/MS is available at Aetrix Electronics and suitable for industrial sensor calibration, legacy PLC configuration storage, and motor drive firmware settings requiring stable component supply, long-life data retention, and drop-in compatibility with existing Microwire designs.

Supply support for 93C66B-I/MS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Microchip Technology Inc. is a leading provider of microcontrollers, analog components, and memory solutions, headquartered in Chandler, Arizona, with global design and manufacturing operations.

The 93Cxx series was designed specifically for cost-sensitive, space-constrained embedded systems requiring reliable nonvolatile storage with minimal external components and legacy interface compatibility.

FAQ

What is the memory organization of the 93C66B-I/MS?

The 93C66B-I/MS has a fixed 256 × 16-bit organization - 4 Kbit total, with no ORG pin. Unlike 'C' variants, it does not support runtime word-size switching. This configuration delivers native 16-bit data access ideal for microcontrollers with 16-bit data buses or ADC interfaces, eliminating software bit manipulation overhead during read/write operations.

Does the 93C66B-I/MS require an external pull-up resistor on the DO pin?

Yes, the 93C66B-I/MS DO pin is open-drain and requires an external pull-up resistor (typically 4.7 kΩ to V_CC) to ensure valid logic-high levels during Read and Ready/Busy status reporting. Without it, DO remains undefined during High-Z states or when driving logic-high, risking communication failure or incorrect busy detection in host firmware.

How is write protection implemented on the 93C66B-I/MS?

The 93C66B-I/MS implements hardware write protection via EWEN (Erase/Write Enable) and EWDS (Erase/Write Disable) commands. It powers up in EWDS mode - all erase/write functions are disabled until EWEN is issued. After any write, issuing EWDS restores protection. This prevents accidental overwrites during power transients or firmware bugs, and is independent of V_CC monitoring circuitry.

What is the minimum V_CC required for ERAL and WRAL operations on the 93C66B-I/MS?

ERAL and WRAL operations on the 93C66B-I/MS require V_CC ≥ 4.5 V - matching its specified operating range. Below this threshold, these commands will not execute correctly, and the device may enter undefined behavior or fail silently. This is enforced by internal voltage detection circuitry; the 93C66B-I/MS does not support ERAL/WRAL at lower voltages unlike some 93LC variants.

Can the 93C66B-I/MS be used interchangeably with the 93C66A-I/MS?

No - the 93C66B-I/MS (256 × 16-bit) and 93C66A-I/MS (512 × 8-bit) have incompatible memory maps and instruction timing. While pinout and interface are identical, READ/WRITE opcodes expect different address widths and data lengths. Using them interchangeably causes misaligned reads, truncated writes, or command timeouts. Software drivers must be reconfigured for word size and address depth.