6.1. Serial Identifier

The serial identifier of all Plug and Play ISA cards is defined below.

Table 2. Plug and Play Header

Field Name	Length	Definition
Vendor ID Byte 0	8 bits	Bit[7] 0 Bits[6:2] First character in compressed ASCII Bits[1:0] Second character in compressed ASCII bits[4:3]
Vendor ID Byte 1	8 bits	Bits[7:5] Second character in compressed ASCII bits[2:0] Bits[4:0] Third character in compressed ASCII
Vendor ID Byte 2	8 bits	(Vendor Assigned) Bits[7:4] First hexadecimal digit of product number (bit 7 is msb) Bits[3:0] Second hexadecimal digit of product number (bit 3 is msb)
Vendor ID Byte 3	8 bits	(Vendor Assigned) Bits[7:4] Third hexadecimal digit of product nmber (bit 7 is msb) Bits[3:0] Hexadecimal digit of revision level (bit 3 is msb)
Serial/Unique Number Byte 0	8 bits	Unique device number so the system can differentiate between multiple cards of the same type in one system. Bits[7:0]
Serial Number Byte 1	8 bits	Serial Number Bits[15:8]
Serial Number Byte 2	8 bits	Serial Number Bits[23:16]
Serial Number Byte 3	8 bit	Serial Number Bits [31:24]
Checksum	8 bits	Checksum of ID and serial number verifies that the information has been correctly read from a Plug and Play ISA card.

6.1.1. Vendor ID

The 32-bit Vendor ID is an EISA Product Identifier (ID). This ID consists of:

bits[15:0] - three character compressed ASCII EISA ID. (See Table 2 for bit definitions.) Compressed ASCII is defined as 5 bits per character, "00001" = "A" ... "11010" = "Z". This field is assigned to each manufacturer by the EISA administrative agent.
bits[31:16] - manufacturer specific product number and revision. (See Table 2 for bit definitions.) It is the responsibility of each vendor to select unique values for this field.

The purpose of this field is to serve as a unique board identifier that allows Plug and Play card selection through the isolation algorithm described earlier.

6.1.2. Serial/Unique Number

The 32-bit serial number is used only in the isolation process for selection of individual Plug and Play ISA cards. This number differentiates between multiple cards with the same Vendor ID when they are plugged into one system. This number must be unique in order to support multiple cards with the same Vendor ID in one system. If this feature is not supported then this field must be returned as "FFFFFFFF." Lack of a unique serial number implies that only one instance of a Vendor ID can be supported in a system.

6.1.3. Checksum

The checksum field is used to ensure that no conflicts have occurred while reading the device identifier information. The checksum generation is described in appendix B.