MA28140 Datasheet, PDF(20/72 Page) Dynex Semiconductor

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MA28140 Datasheet, PDF (20/72 Pages) Dynex Semiconductor – Packet Telecommand Decoder

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MA28140

CHANGE PROGRAMMABLE KEY BLOCK CONTROL

COMMANDS A AND B

Two such Control Commands are provided to cover the full

size of the Programmable Key:

- Command A concerns the first 256 octet boundaries.

- Command B concerns the last 112 octet boundaries.

It is possible to load a 5-octet (40 bits) block starting from

any of the 368 octet boundaries. Any transmission using the

unused boundaries of Command B (from 113 to 255) is

ignored and reported as non-executable. The key used for

authenticating the TC Segment containing one of these

Control Commands will be whatever key was selected in the

AU at the time each Control Command was received. Once the

TC Segment has been authorized by the authentication

process, the TC Segment, minus the 40-bit signature s (i.e.

[m,l]) is complemented and passed once more through the

signature-building process, i.e. through the Authentication

Processor. The 24 bits of virtual fill z are inserted as before,

i.e., they are not complemented, but remain all zeros. The

result of the process is a 40-bit pseudo-signature which,

instead of being sent to the Signature Comparator, is loaded in

the Programmable Key memory, starting at the octet location

indicated by the start address field, as follows:

- Bits 32 through 39 of pseudo-signature at the indicated

octet location;

- Bits 24 through 31 of pseudo-signature at the next

location (start address + 1);

- And so on, until Bits 0 through 7 are loaded at location

start address + 4.

Any arbitary procedure can be used for changing the key,

starting from any of the 368 octet boundaries.

RAM

Mapping

200

201

202

203

204

205

206

207

2FF

300

367

368

369

36A

36B

36C

36D

36E

36F

Address provided in the

Control command (decimal)

000 40

W0 (40 to 47)

001 32

W0 (32 to 39)

002 24

W0 (24 to 31)

003 16

W0 (16 to 23)

004 8

W0 (8 to 15)

005 0

W0 (0 to 7)

006 40

W1 (40 to 47)

007 32

W1 (32 to 39)

255 16

000 8

W42 (16 to 23)

W42 (8 to 15)

103 0

104

105 55

106 47

107 39

108 31

109 23

110 15

111 7

W59 (0 to 7)

59 C (59 to 56) 56

C (55 to 48)

C (47 to 40)

C (39 to 32)

C (31 to 24)

C (23 to 16)

C (15 to 8)

C (7 to 0)

0 Note: Bit 0 is the MSB

Figure 9: Organisation of the Programmable Key Memory

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