User`s manual

EEPROM Control

The cpuModule is equipped with an EEPROM, or "Electrically Erasable and Programmable Read

Only Memory". This part is primarily used to store the configuration from the Setup program. You

can also use this part for non-volatile storage of a small amount of data. Its contents are retained even

with system power off and no backup battery connected.

The EEPROM consists of 1024 bits organized as 64 words of sixteen bits each. Thirty-two words

are used by the BIOS to store Setup information. The remaining 32 words are available to your ap-

plications. You may access these memory locations using functions of software interrupt 52H, which

are listed below.

NOTE!

The EEPROM will wear out after a large number of write cycles. You

should not use the EEPROM to hold data which is updated frequently.

To prevent unintended changes to the Setup stored in the EEPROM,

we recommend you always access the EEPROM using the interrupt

functions listed below

Function 0 EEPROM write/erase enable. It is active until the next disable

command and allows the device to be written and erased.

INPUTS: AH = 0

RETURNS: AH = error code

Function 1 EEPROM write/erase disable. This instruction must always be the

last operation performed, to prevent undesired EEPROM access.

INPUTS: AH = 1

RETURNS: AH = error code

Function 2 EEPROM read. Reads from the device address specified in AL the

number of words specified in CX, then stores the read values into

the buffer addressed by ES:DI

INPUTS: AH = 2

AL = address (0-3FH accepted)

CX = number of words to read

ES:DI = pointer to the buffer where the read values are stored

RETURNS: AH = error code; if AH<>0, then AL = number of locations read

Function 3 EEPROM write. Writes at the device address specified in AL, for

the number of words specified in CX, the values pointed by DS:SI.

Does not allow write operations at locations 0 to 1FH, which are

reserved.