Core3DES
Pause/Resume
For normal operation, the EN input is held at a logic '1'
value. The core can be paused by holding the EN input at
a logic '0' value, indefinitely, as shown by the example in
Figure 10 where cycle 3 of an encryption operation is
paused. To resume operation, the EN input should be
brought back to a logic '1' value. This functionality
applies to either encryption or decryption. Note that the
ED input must remain at logic '1' throughout an entire
encryption cycle or at logic '0' throughout an entire
decryption cycle; otherwise, unpredictable results on the
Q[1:64] outputs will occur.
clock cycles to encrypt the next block. After all blocks of
data are encrypted, the user would then need to hold
the EN input at a logic '0' value, since if it is left at a logic
'1', data will continue to be encrypted ad infinitum.
When ready for the next blocks of data, the user can
then resume the encryption process by holding the EN
input at a logic '1' value. Another possible use may be if
the user has an elastic buffer (FIFO) connected to the
Q[1:64] outputs. If the FIFO is filling up with encrypted
data faster than the encrypted data is being read out of
the FIFO, the user may wish to pause the Core3DES
macro by setting the EN input to a logic '0' when the full
or almost-full flag logic from the FIFO is active. When the
FIFO full or almost-full flag logic clears, the Core3DES
macro can then resume operation by again setting the
EN input to a logic '1' value.
The pause/resume functionality is provided as an aid to
the user. One possible use for the pause functionality is a
case where many blocks of data are encrypted one after
another. The EN input would be held statically at a logic
'1' value, and the data input needs to change every 48
cycle 3
"paused"
...
...
...
47 48 49 50
cycle
1
2 3a 3b 3c
4
5
15 16 17 18
31 32 33 34
CLK
K[1:64]
D[1:64]
ED
ck1
d1
ck2
ck3
ck1
d2
EN
00
00 01
01 10
10 00
KSEL[1:0]
q1
Q[1:64]
QVAL
Undefined
Don't care
Figure 10 • Example Encryption Pause/Resume Sequence
v5.0
9
ACTEL [ Actel Corporation ]
