WM710xx – Secure F-RAM with Gen-2 RFID
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- Description
LOCK
0
0
0
1
Register unlocked. All control bits, including the LOCK and PERMALOCK bits
can be written to from the OPEN or SECURED states.
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.
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
0
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)
230
4k
8k
xxx
xxx
000
001
010
011
100
101
110
110
x
x
486
16k
16k
16k
16k
16k
16k
16k
16k
1
931
2
963
4
979
8
987
16
32
64
128
991
993
993
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.
Wrap Enable: Asserting the WRPEN control bit to a logic one enables the USER memory wrapping feature.
The wrap enable feature allows the stored address pointer to wrap back to the factory-set initial stored address
value of 0x006. In this manner, the WM710xx memory acts as a circular buffer. Clearing the WRPEN control
bit disables wrapping resulting in a write-once memory. In this case, when the Working Stored Address
reaches the end of user memory, no additional unaddressed write cycles will be possible. The WRPEN and
Rev. 1.2
Sept. 2010
Page 8 of 17
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
