Chapter 4. Data Encryption Standard Execution Unit
4-3
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Operational Registers
Table 4-3 describes DCFG fields.
4.1.3 DEU Status Register (DSR)
The status register contains bits that give information about the state of the DEU. There are
two bits which state when more input can be written to the input data register and read from
the output data register. To maximize throughput, data is buffered, and reading and writing
can be overlapped. When the IRDY bit is one, new data can be written to the input
(DATA_IN) registers. It is possible to write three 64-bit blocks of data before any output
data is read (and the IRDY signal goes low).
Figure 4-3 shows the DES status register.
Figure 4-3. DES Status Register (DSR)
Table 4-4 describes DSR fields.
Upon completion of an encryption (or decryption), the ORDY signal will go high,
indicating that the output is ready to be read from the DATA_OUT registers. If interrupts
are enabled, then IRQ will be asserted. After the ORDY signal goes high, new data in the
Table 4-3. DCFG Field Descriptions
Bits
Name
Description
0–29
—
Reserved, should be cleared.
30
RST
The DES can be reset by asserting the RESET signal or by setting the Software Reset bit in
the Control Register. The software and hardware resets are functionally equivalent. The
software reset bit will clear itself one cycle after being set.
0 —
1 software reset
31
IMSK
Clearing the interrupt mask bit will allow interrupts on the IRQ pin. It does not affect the IRQ
bit in the status register. This bit is set (interrupts disabled) any time a hardware/software
reset is performed. The user must clear this bit to enable hardware interrupts.
0 enable interrupts
1 disable interrupts
0
29
30
31
Field
—
IDRY ORDY
Reset
0000_0000_0000_0000
R/W
R
Addr
0x201
Table 4-4. DSR Field Descriptions
Bits
Name
Description
0–29
—
Reserved, should be cleared.
30
IRDY
Input Ready. Input Buffer ready to accept more data.
31
ORDY
Output Ready. Output Buffer has data to send.
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Freescale Semiconductor, Inc.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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