56.5.2 TDES Mode Register

This register can only be written if the WPEN bit is cleared in the TDES Write Protection Mode Register.

Name:	TDES_MR
Offset:	0x04
Reset:	0x00000002
Property:	Read/Write


Bit	31	30	29	28	27	26	25	24
	TAMPCLR
Access	R/W
Reset	0


Bit	23	22	21	20	19	18	17	16
							CFBS[1:0]
Access							R/W	R/W
Reset							0	0


Bit	15	14	13	12	11	10	9	8
	LOD		OPMOD[1:0]				SMOD[1:0]
Access	R/W		R/W	R/W			R/W	R/W
Reset	0		0	0			0	0


Bit	7	6	5	4	3	2	1	0
	PKRS	PKWO		KEYMOD		TDESMOD[1:0]		CIPHER
Access	R/W	R/W		R/W		R/W	R/W	R/W
Reset	0	0		0		0	1	0

Bit 31 – TAMPCLR Tamper Pin Clear Key Enable

Value	Description
0	A tamper detection event has no effect on TDES_KEYxWRy.
1	A tamper detection event immediately clears TDES_KEYxWRy.

Bits 17:16 – CFBS[1:0] Cipher Feedback Data Size

Value	Name	Description
0	SIZE_64BIT	64 bits
1	SIZE_32BIT	32 bits
2	SIZE_16BIT	16 bits
3	SIZE_8BIT	8 bits

Bit 15 – LOD Last Output Data Mode

Warning: In DMA mode, reading to TDES_ODATARx before the last data encryption/decryption process may lead to unpredictable result.

Value	Description
0	No effect. After each end of encryption/decryption, the output data is available either on TDES_ODATARx (Manual and Auto modes) . In Manual and Auto modes, the DATRDY flag is cleared when at least one of the TDES_ODATARx is read.
1	The DATRDY flag is cleared when at least one of the Input Data Registers is written. No further TDES_ODATARx reads are necessary between consecutive encryptions/decryptions (see Last Output Data Mode).

Value

Description

No effect.

After each end of encryption/decryption, the output data is available either on TDES_ODATARx (Manual and Auto modes) .

In Manual and Auto modes, the DATRDY flag is cleared when at least one of the TDES_ODATARx is read.

The DATRDY flag is cleared when at least one of the Input Data Registers is written.

No further TDES_ODATARx reads are necessary between consecutive encryptions/decryptions (see Last Output Data Mode).

Bits 13:12 – OPMOD[1:0] Operating Mode

For CBC-MAC operating mode, set OPMOD to CBC and LOD to 1.

Value	Name	Description
0	ECB	Electronic Code Book mode
1	CBC	Cipher Block Chaining mode
2	OFB	Output Feedback mode
3	CFB	Cipher Feedback mode

Bits 9:8 – SMOD[1:0] Start Mode

If a DMA transfer is used, 0x2 must be configured. See DMA Mode for more details.

Value	Name	Description
0	MANUAL_START	Manual mode
1	AUTO_START	Auto mode
2	IDATAR0_START	TDES_IDATAR0 accesses only Auto mode

Bit 7 – PKRS Private Key Internal Register Select

Value	Description
0	The keys used by the TDES are in the TDES_KEY1WRx, TDES_KEY2WRx and TDES_KEY3WRx registers.
1	The keys used by the TDES are the in the Private Key internal registers written through the Private Key bus.

Bit 6 – PKWO Private Key Write Once

Once PKWO is set to ‘1’, only a hardware reset sets this bit to ‘0’ internally. Writing it to ‘0’ with a register access has no impact (although the field will be read to value ‘0’).

Value	Description
0	The Private Key internal register can be written multiple times through the Private Key bus.
1	The Private Key internal register can be written only once through the Private Key bus until hardware reset.

Bit 4 – KEYMOD Key Mode

Value	Description
0	Three-key algorithm is selected.
1	Two-key algorithm is selected. There is no need to write TDES_KEY3WRy (or Private Pey internal registers with more than 128 bits).

Bits 2:1 – TDESMOD[1:0] ALGORITHM Mode

Values which are not listed in the table must be considered as “reserved”.

Value	Name	Description
0	SINGLE_DES	Single DES processing using TDES_KEY1WRy.
1	TRIPLE_DES	Triple DES processing using TDES_KEY1WRy, TDES_KEY2WRy and TDES_KEY3WRy .
2	XTEA	XTEA processing using TDES_KEY1WRy and TDES_KEY2WRy.

Bit 0 – CIPHER Processing Mode

Value	Name	Description
0	DECRYPT	Decrypts data.
1	ENCRYPT	Encrypts data.