AT27C256R-55PC Equivalent & Substitute Parts

Part Overview

The AT27C256R-55PC is a 256Kbit parallel EPROM (Erasable Programmable Read-Only Memory) manufactured by Microchip Technology in a 28-DIP package with 55 ns access time. This part is classified as obsolete, which necessitates identification of functionally equivalent alternatives for ongoing system support and new designs. The obsolete status indicates limited availability and potential discontinuation, making substitute parts critical for procurement planning and system maintenance.

Substiute Parts

AT27C256R-55PC

Microchip TechnologyIn Stock: 996AT27C256R-55PC Datasheet

Current PartRFQ

AT27C256R-70PU

Microchip TechnologyIn Stock: 6959AT27C256R-70PU Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the AT27C256R-55PC is determined by the following critical parameters that must remain constant or compatible:

Mandatory Matching Parameters:

• Memory Type: Non-Volatile EPROM
• Memory Size: 256Kbit
• Memory Organization: 32K x 8
• Memory Interface: Parallel
• Package / Case: 28-DIP (0.600", 15.24mm)
• Mounting Type: Through Hole
• Voltage Supply: 4.5V ~ 5.5V

Allowable Variation Parameters:

• Access Time: May be equal or faster (lower ns value acceptable)
• Operating Temperature: May be wider range (extended temperature acceptable)
• Product Status: Active status preferred for availability
• RoHS Compliance: May differ based on application requirements

The AT27C256R-70PU qualifies as a direct substitute because it maintains all mandatory parameters while offering improved specifications in access time tolerance and operating temperature range, with active product status and enhanced compliance certifications.

Parameter Comparison

Engineering Selection Recommendations

The AT27C256R-70PU is the qualified substitute for the AT27C256R-55PC based on the following engineering criteria:

Product Availability: The substitute part maintains active product status with 6905 units in stock, compared to the obsolete status of the original part with 957 units. Active status ensures long-term procurement viability.

Compliance Posture: The AT27C256R-70PU achieves ROHS3 compliance, whereas the original part is RoHS non-compliant. This compliance improvement aligns with current regulatory requirements for electronic components in regulated markets.

Functional Compatibility: Both parts share identical memory capacity (256Kbit), organization (32K x 8), interface type (Parallel), supply voltage (4.5V ~ 5.5V), and physical package (28-DIP). The substitute operates within the same electrical environment as the original design.

Performance Consideration: The access time increases from 55 ns to 70 ns. This 15 ns difference is acceptable in applications where the original 55 ns specification was not a critical timing constraint. Systems with timing-critical requirements must evaluate whether the extended access time impacts overall system performance.

Temperature Range: The substitute provides an extended operating temperature range (-40°C ~ 85°C) compared to the original (0°C ~ 70°C), offering greater flexibility for applications requiring wider temperature operation.

Frequently Asked Questions (FAQ)

Q: Can the AT27C256R-70PU directly replace the AT27C256R-55PC in existing designs?

A: Yes, for most applications. Both parts are pin-compatible 28-DIP packages with identical memory capacity and organization. The primary consideration is the access time difference (55 ns vs. 70 ns). If your system timing does not depend on the faster 55 ns specification, the substitute is functionally equivalent.

Q: What is the significance of the access time difference between 55 ns and 70 ns?

A: Access time defines the maximum delay from address input to valid data output. The 70 ns specification is slower than 55 ns. In most legacy systems, this difference is negligible. However, in timing-critical applications where data must be available within specific nanosecond windows, this 15 ns increase may require system-level timing analysis.

Q: Why is the AT27C256R-55PC obsolete?

A: EPROM technology has been superseded by more modern non-volatile memory technologies. Microchip has transitioned production away from this product line. The obsolete status means the manufacturer no longer actively produces or supports this part.

Q: Are there any package or pinout differences between these parts?

A: No. Both parts use the 28-DIP (0.600", 15.24mm) package with identical pinout. They are mechanically and electrically interchangeable at the socket level.

Q: Does the extended temperature range of the substitute affect compatibility?

A: No. The substitute's extended range (-40°C ~ 85°C) is a superset of the original range (0°C ~ 70°C). Any application operating within the original temperature limits will function correctly with the substitute.

Q: What does ROHS3 compliance mean for the substitute part?

A: ROHS3 compliance indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting lead and other hazardous materials. This is relevant for applications subject to EU regulations or customer requirements mandating RoHS compliance.

Q: Is the substitute part programmable through DiGi-Electronics?

A: The substitute (AT27C256R-70PU) is verified as programmable through DiGi-Electronics, whereas the original part's programmability status is not verified. This provides additional assurance for programming and verification workflows.