Microchip Technology AT91M55800A-33AU – ARM7TDMI 16-/32-bit MCU, ROMless, 33 MHz, 176‑LQFP (Obsolete)
The Microchip Technology AT91M55800A-33AU is a legacy member of the AT91 family built around the ARM7TDMI 16-/32-bit RISC core. Operating up to 33 MHz and delivered in a 176‑lead LQFP package, this ROMless microcontroller is designed to execute code from external program memory. While the device is now obsolete and not recommended for new designs, it remains relevant for sustaining engineering, maintenance of deployed equipment, and controlled redesigns where maintaining software or hardware compatibility is critical.
Engineers value the AT91M55800A-33AU for its straightforward ARM7TDMI architecture and predictable performance profile, while sourcing managers appreciate the clear part suffixing (AU = lead-free) and defined package and mounting details that help avoid errors in last-time-buys and aftermarket procurement.
Important correction: Some listings have erroneously associated this MPN with ARM9/ARM926 cores. This is incorrect. The AT91M55800A-33AU is based on the ARM7TDMI core, consistent with Microchip’s AT91M family.
Highlights
- Brand and series: Microchip Technology, AT91 family
- CPU core: ARM7TDMI (16-/32-bit RISC)
- Max clock frequency: 33 MHz
- Program memory: ROMless (executes from external program memory)
- Package: 176‑LQFP; packaging supplied in tray
- Mounting: Surface mount
- Lifecycle status: Obsolete / not recommended for new designs
- RoHS: RoHS compliant; AU suffix indicates lead-free finish (verify per lot)
Key specifications at a glance
- Manufacturer part number (MPN): AT91M55800A-33AU
- Category: Microcontrollers (MCU)
- Architecture: 16-/32‑bit, ARM7TDMI core
- Maximum operating frequency: 33 MHz
- Program memory type: ROMless (requires external memory)
- Package / case: LQFP‑176
- Pin count: 176
- Mounting type: Surface mount
- Packaging: Tray
- RoHS status: RoHS compliant (confirm via supplier documentation)
- Lifecycle: Obsolete
Items not specified in the available documentation: on‑chip SRAM/EEPROM size, peripheral set, I/O count per port, operating temperature range, power consumption figures, and timing parameters. Refer to the official datasheet for these details.
Where this device fits
The AT91M55800A-33AU is suited to legacy designs and sustaining programs where the original platform expects an ARM7TDMI-class MCU executing from external memory. Typical contexts include:
- General embedded control in mature or long-lifecycle products
- AT91 platform-based systems that were architected for ROMless execution
- Industrial equipment and automation systems undergoing maintenance or limited feature refresh
Because the device is obsolete, its primary value lies in compatibility and service continuity, rather than as a candidate for new program starts.
Architecture and design considerations
- ARM7TDMI core: A proven 16-/32‑bit RISC architecture widely used in legacy embedded systems. It offers a predictable execution profile suitable for real-time control tasks typical of older AT91 platforms.
- ROMless execution: The device is intended to fetch and execute code from external program memory. When servicing or redesigning boards, verify the external memory interface, signal integrity, and boot sequencing that your existing design relies on. Memory timings, bus loading, and device selection logic are central to system stability.
- 33 MHz ceiling: System timing, peripheral clocks, and memory access latencies in existing designs will have been validated around this maximum frequency. When replacing units or requalifying boards, maintain clock sources and dividers consistent with the original design constraints.
- 176‑LQFP footprint: High pin count allows for broad bus connectivity and board-level routing options. For repairs or remanufacture, confirm the land pattern, solder stencil thickness, and reflow profile with your CM, especially when mixing legacy boards with lead-free device variants.
Note: Detailed bus, peripheral, and timing parameters are not specified here and must be taken from the official datasheet.
Package, mounting, and handling
- Package: LQFP‑176, surface mount
- Delivery: Tray
- Handling: As an LQFP device, standard ESD and moisture sensitivity precautions apply. Follow your facility’s MSL procedures and store/handle trays per supplier instructions. Specific MSL classification is not provided here; consult the datasheet and packaging labels.
Applications and use cases
- General embedded control where code executes from external memory
- Industrial/legacy systems built on the AT91 platform
- Equipment requiring long-term service support and form/fit/function continuity
For new designs, select a current-generation microcontroller that meets performance, power, and integration targets. The AT91M55800A-33AU is not recommended for fresh development due to its obsolete status and limited availability.
Lifecycle and sourcing guidance
- Lifecycle status: Obsolete
- Availability: Limited. Inventory quantity is reported as zero in current data. Expect sporadic supplies through surplus or aftermarket channels.
- Sourcing tips for sustaining builds:
- Order by the full MPN (AT91M55800A-33AU) to capture the correct frequency grade and the AU lead-free suffix.
- Request traceability and RoHS certificates; confirm the AU suffix and finish details on labels and certificates of conformance.
- Inspect for date code ranges consistent with your qualification and any internal component control plans.
- Validate incoming parts with visual inspection and electrical screening when purchasing from non-franchised channels.
Because the device is obsolete, consider last-resort procurement approaches (authorized distributor obsolete stock, reputable aftermarket distributors) and plan for a structured migration.
Replacements and migration planning
- Direct replacements: None specified. No pin- or function-compatible alternatives are listed in the available data.
- Migration strategy:
- Evaluate modern microcontrollers that meet your functional requirements (performance, memory, I/O, and interfaces) and long-term availability targets.
- If staying within the Microchip ecosystem is desirable, assess contemporary families documented on Microchip’s website. Align choices with available development tools, software libraries, and longevity commitments. Specific substitute part numbers are not provided here.
- Plan for software porting: ROMless ARM7TDMI codebases may require toolchain updates, endianness checks, peripheral driver rewrites, and memory map refactoring when moving to any new architecture.
- Hardware updates: Expect board changes when moving away from a 176‑pin LQFP to a different package or when migrating from an external program memory architecture to integrated Flash MCUs.
When an exact drop-in is not available, manage risk via prototyping, A/B builds, and a clear qualification plan covering EMC, environmental, and reliability testing.
Compliance and environmental notes
- RoHS: Reported as RoHS compliant. The AU suffix indicates a lead-free finish. Always verify compliance per lot using supplier documentation and certificates of conformity.
- Environmental ratings: Not specified in the provided data (temperature range, shock/vibration, etc.). Consult the datasheet for detailed environmental and reliability parameters relevant to your product’s qualification profile.
Procurement essentials
- Full identification: Microchip Technology AT91M55800A-33AU
- Series and category: AT91 series, Microcontrollers (MCU)
- Package and shipping: 176‑LQFP, supplied in tray
- Mounting: Surface mount
- Status: Obsolete / not recommended for new designs
- Pricing: Typically available by quote only in aftermarket channels; expect variability due to scarcity
To minimize delays, include the complete MPN and any internal AVL references on purchase orders, and align receiving inspection with your obsolescence control plan.
Accuracy note: core identification
Some third-party listings have attributed ARM926EJ‑S to this MPN. That is incorrect. Per the part family and available product documentation, the AT91M55800A‑33AU is ARM7TDMI-based. Always verify part family and core type against the official Microchip datasheet when resolving BOM discrepancies or preparing deviations/waivers.
Frequently asked questions (FAQs)
- What CPU core does the AT91M55800A-33AU use?
- ARM7TDMI (16-/32‑bit RISC).
- Does this device include on‑chip Flash program memory?
- No. It is a ROMless device intended to execute from external program memory.
- What is the maximum operating frequency?
- Up to 33 MHz.
- What is the package and pin count?
- 176‑lead LQFP, 176 pins total.
- Is the AT91M55800A-33AU RoHS compliant?
- Yes, reported as RoHS compliant. The AU suffix denotes a lead-free finish. Confirm compliance per lot with supplier documentation.
- Is it suitable for new designs?
- No. It is obsolete and not recommended for new designs.
- What are the operating temperature range and power consumption figures?
- Not specified in the provided data. Refer to the Microchip datasheet for exact specifications.
- Are there direct drop‑in replacements?
- None are specified. Evaluate modern alternatives and plan for hardware/software migration if replacement is required.
- Why do some sources mention ARM926 or ARM9?
- That is a common mislisting. This MPN belongs to the ARM7TDMI-based AT91 family.
Resources
- Product page: https://www.microchip.com/en-us/product/AT91M55800A
- Datasheet: https://www.microchip.com/en-us/product/AT91M55800A
In summary, the Microchip Technology AT91M55800A-33AU is a ROMless ARM7TDMI-based MCU in a 176‑pin LQFP package, operating up to 33 MHz and supplied lead-free (AU suffix). Although obsolete, it remains important for sustaining engineering of legacy AT91 designs that depend on external program memory and a stable ARM7TDMI execution environment. For new projects, select a current, supported MCU family aligned with your performance, integration, and longevity goals, and use the official Microchip documentation to guide specification, sourcing, and migration decisions.