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Method for detecting the addressing scheme for PROM on an add-in card

IP.com Disclosure Number: IPCOM000010227D
Publication Date: 2002-Nov-06
Document File: 4 page(s) / 87K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for detecting the addressing scheme for programmable read-only memory (PROM) on an add-in card. Benefits include improved functionality and improved design flexibility.

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Method for detecting the addressing scheme for PROM on an add-in card

Disclosed is a method for detecting the addressing scheme for programmable read-only memory (PROM) on an add-in card. Benefits include improved functionality and improved design flexibility.

Background

        � � � � � For graphics memory controller hubs (GMCHs) to support display flexibility via accelerated graphics processor digital display (ADD) cards, they must have a PROM device that contains identification and initialization information. However, conventional PROMs may use a variety of addressing schemes, which are not overlapping. Some examples are byte (8-bit), byte and a half (11 bits), and two bytes (16 bits) for the address index. The different address schemes are used with PROMs of various sizes and costs. For example, PROMs that use byte addressing can only be up to 256 bytes but are typically inexpensive. PROMs that use byte-and-a-half addressing can be up to 2 kilobytes but are generally more expensive than a byte-addressed PROM.

� � � � � The capability to use a variety of PROM types is conventionally not required. Typically, PROMs contain a fixed set of information, utilizing one addressing scheme. However, communicating with PROMs of different address schemes requires the GMCH and its software to support and utilize those different addressing schemes. Because they are not necessarily directly compatible with each other, conflicts may arise if the GMCH does not know which addressing scheme to employ. For example, when the GMCH is in 2-byte address mode but the PROM uses byte or byte-and-a-half addressing, the identification and configuration processes can fail. If the GMCH is in 2-byte mode, it sends out two full bytes of what it considers is the index. If the PROM is a byte or byte-and-a-half addressed PROM, it sees the first byte as an index and the second byte as a separate data-write transaction. Because of this misalignment, the GMCH and PROM are no longer synchronized. Data in the PROM may be incorrectly written over, or the incorrect data may be read back from the PROM.

        � � � � � To avoid conflicts, the add-in card (with a populated PROM) must relay the appropriate addressing scheme to the GMCH and its software. ADD cards and the listed GMCHs accomplish this by embedding the PROM addressing scheme within the ADD_ID straps. Because these signals are intended to provide card identification information to the GMCH, the PROM addressing information is embedded in these signals as well.

General description

        � � � � � The disclosed method enables detection and support for a wide variety of PROM types. Because ADD cards provide a flexible environment in terms of requirements for identification and initialization, flexibility in PROM sizes, types, and cost is a requirement.

Advantages

        � � � � � Some implementations of the disclosed structure and method provide one or more of the following advantages:

•        � � � � Improved functionality due to enabling a GMCH and its s...