C6678 DDR3 termination

g.f.

Hi,

I have a question about C6678 DDR3 I/F.

Is there any termination inside the C6678 DDR3.
In C6678 IBIS model, it is written like follow:
* Rx mode, 45 ohm Half Termination (90ohm to Vtt)
* Rx mode 50 ohm Full Termination (50ohm to Vtt)

Is this means that there are either 45 or 50 ohm termination inside the C6678?

best regards,
g.f.

over 12 years ago

0 Bill Taboada over 12 years ago

TI__Mastermind 42545 points

DDR3 includes on die termination (ODT) for the data bus interface. The termination in the DDR memory is used for write accesses. The termination in the C667x is used for reads. Currently the documentation for the DDR3 controller states that the ODT for reads should always be full Thevenin termination.

0 g.f. over 12 years ago in reply to Bill Taboada

Guru 15520 points

Hi, Bill

Thank for the answer.

I understand that there is termination in the C667x and used for read.
So, is the termination value 50 ohm?

By the way, I checked the DDR3 Controller User's Guide(SPRUGV8C),
but can't find that the ODT for reads should always be full Thevenin termination.
Where is it written?

best regards,
g.f.

0 Bill Taboada over 12 years ago in reply to g.f.

TI__Mastermind 42545 points

Hi g.f.

The impedance is determined by the value of the resistor you have connected to you PTV pin. If you have the recommended 45.3 ohm resistor you will have a full Thevenin termination with 45ohms to VTT.

The full Thevenin is selected by default by placing a 0x1 in the RD_LOCKAL_ODT field in the DDR_PHY_CNTL_1 registers. You can find this in Table 4-25 of the DDR3 Memory Controller Users Guide.

Regards, Bill

0 g.f. over 12 years ago in reply to Bill Taboada

Guru 15520 points

Hi Bill,

Thank you so much.

I now understand.

best regards,

g.f.

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C6678 DDR3 termination