48LM01-ISLASHSM datasheet(9/40 Pages) MICROCHIP

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DS20006008C-page 9

48L512/48LM01

3.0

MEMORY ORGANIZATION

3.1

Data Array Organization

The 48L512/48LM01 is internally organized as a

continuous SRAM array for both reading and writing,

along with a nonvolatile EEPROM array that is not

directly accessible to the user, but which can be

refreshed or recalled on power cycles or on software

commands.

The

SRAM

array

continuously

addressable, so the entire array can be written without

having to access pages.

3.2

16-Byte Nonvolatile User Space

The 48L512/48LM01 devices contain a 16-byte

nonvolatile user space, separate from the SRAM

memory array. The nonvolatile user space can be

written with the Write Nonvolatile User Space

(WRNUR) command and read with the Read

Nonvolatile User Space (RDNUR) command. Once

written, these 16 bytes remain volatile and can be

rewritten. They are copied to nonvolatile memory – at

the same time as the SRAM array and STATUS register

– automatically on any power disruption or by using the

Software Store command described in Section 11.0

“Store/Recall Operations”.

Reading and writing to the nonvolatile user space does

not use address bits, only the specific access

instruction to precede the operation. Writing to the

nonvolatile user space requires writing all of its bits in

one operation. Failing to write to all nonvolatile user

space bits will abort the write operation and leave the

nonvolatile user space value unchanged from its

previous value. Similarly, reading the nonvolatile user

space memory uses no address bits, but partial reads

are allowed.

3.3

Device Registers

The 48L512/48LM01 contains a STATUS register for

controlling and monitoring functions of the device.

3.3.1

STATUS REGISTER

The STATUS register is an 8-bit combination of writable

and read-only bits. It is used to modify the write

protection functions as well as store various aspects of

the current status of the device. The writable bit values

written to the STATUS register are volatile – until they

are copied to nonvolatile memory automatically on any

power disruption or by using the Software Store

command described in Section 11.0 “Store/Recall

Operations” – and can be overwritten from a previous

status in a recall operation. Details about the STATUS

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