DS1855

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MEMORY ORGANIZATION

The DS1855’s serial EEPROM is internally organized with 256 words of 1 byte each. Each word requires

an 8-bit address for random word addressing. The byte at address F9h determines the wiper setting for

potentiometer 0, which contains 100 positions. Writing values above 63h to this address sets the wiper to

its uppermost position, but the MSB is ignored. The byte at address F8h determines the wiper setting for

potentiometer 1, which contains 256 positions (00h to FFh). Address locations FAh though FFh are

reserved and should not be written.

MEMORY

LOCATION

NAME OF

MEMORY

LOCATION

FUNCTION OF MEMORY LOCATION

00h – F7h

User Memory

General-purpose user memory.

F8h

Potentiometer 1 Setting Writing to this byte controls the setting of potentiometer 1, a 256-

position pot. Valid settings are 00h to FFh.

F9h

Potentiometer 0 Setting Writing to this byte controls the setting of potentiometer 0, a 100-

position pot. Valid settings are 00h to 63h. MSB is ignored.

FAh

Software Lock

Configuration Byte

The three lower bits in this byte can be used to set write-protection

to the 256-byte memory block.

B2: Writing this bit to a 1 protects the upper page of memory. If

this bit is set, memory locations F8h to FFh are configured for

write-protection.

B1: Writing this bit to a 1 protects the upper block of memory. If

this bit is set, memory locations 80h to F7h are configured for

write-protection. The upper page must be unlocked in order to

modify the locking of this portion of memory.

B0: Writing this bit to a 1 protects the lower block of memory. If

this bit is set, memory locations 00h to 7Fh are configured for

write-protection. The upper page must be unlocked in order to

modify the locking of this portion of memory.

B2 B1 B0