WM710xx – Secure F-RAM with Gen-2 RFID

Rev. 1.4

May 2011

Page 11 of 24

Upon power up, WM710xx‟s control logic reads the Control/Status word out of memory and configures itself

accordingly. User applications may change the Control Word as needed providing the register has not been

permanently locked. The Control/Status word may be read by the application at any time.

Register Locking: The LOCK and PERMALOCK control bits are implemented in a similar manner as locking

bits used for Gen2 memory bank locking with the exception that the lock control bits are incorporated into the

register they are locking. As such, attention needs to be placed on how the contents of the Control/Status word

are written when the register is not completely unlocked.

Table 4: Control/Status Word Locking

LOCK

PERMA-

LOCK

Description

0

0

Register unlocked. All control bits, including the LOCK and PERMALOCK bits can

be written to from the OPEN or SECURED states.

0

1

Register permanently unlocked. All control bits can be written from the OPEN or

SECURED states. The LOCK and PERMALOCK bits must be set to logic values 0

and 1 respectively when writing the Control/Status word.

1

0

Register locked. All control bits can be written to only from the SECURED state.

The register cannot be written to in the OPEN state. The LOCK and PERMALOCK

bits must be set to logic values 1 and 0 respectively when writing the Control/Status

word.

1

1

Register permanently locked. The register cannot be written in any circumstance.

Block Write Enable: The BLKWREN control bit enables usage of the WM710xx custom command

BLOCKWRITE. The BLKWREN parameter is internally updated during power-on WM710xx initialization.

In the event the host application toggles the state of BLKWREN, a WM710xx power cycle is required to reflect

the change.

Block Size: The 3 BLKSIZ[2:0] control bits adjust the USER memory block sizes as shown in Table 5:. This

provides the RFID application the ultimate flexibility in determining a balance between the USER memory

requirements and the granularity of the number of USER memory words per block. For the WM71016, the

larger the granularity of the block size, the greater amount of available USER memory; block size has no effect

on WM71004 or WM71008 memory. The effect of the block size on available USER memory is shown in

Table 1. The total number of USER memory words available as a function of the block size is shown in Table 5

below. It is of utmost importance that the 3-bit block size is not modified once set, which would result in

corruption of block permalock status bits.

Table 5: Available USER Memory

Memory

BLKSIZ

Words/Block

Free USER Memory

(words)

4k

xxx

x

230

8k

xxx

x

486

16k

000

1

931

16k

001

2

963

16k

010

4

979

16k

011

8

987

16k

100

16

991

16k

101

32

993

16k

110

64

993

16k

110

128

993

Wrap Status: The WRPSTAT status bit is asserted to a logic one when the following conditions are true:

(a) WRPEN=1, AUTOINCR=1 and AUTOLOCK=0,

(b) The contents of the Working Stored Address register address the last USER memory location, and

(c) An unaddressed WRITE command is received.

The WRPSTAT can be cleared by the RFID interrogator by writing a logic zero to the WRPSTAT bit.