TMS320C6747: Calculating T_RAS_MAX

Anthony Monti

Part Number: TMS320C6747

Tool/software:

I have a SDRAM on the EMIFB and the refresh rate is 16 ms and 4096 rows.

The tRAS_MAx is 120k ns, and I viewing Table 19-22 in document SPRUH91D–March 2013–Revised September 2016

The formula for T_RAS_MAX for EMIFB.SDTIM2 bits 30-27 (4 bits wide) is:

T_RAS_MAX = (tRAS_Max / SDRAM refresh rate) -1

I'm using 16ms/4096 for the SDRAM refresh rate = 3.90625 us.

T_RAS_MAX = (120 us / 3.90625 us ) -1 = 29.72 a number too big for the 4 bit field.

Any suggestions?

Thank you, Tony

0 PaulM 9 months ago

Tony

I'll check this and get back to you shortly

--Paul

0 PaulM 9 months ago in reply to PaulM

Tony

I went through the math and came to the same result as you.

However, Table 19-22 does have a note against this formula that reads:

1) Register field value must be ≤ the calculated value

So the register value can be no larger than the calculated value, but can be smaller.

In your case, the maximum number of refresh_rate intervals from Activate to Precharge command would be 16. Would this work?

--Paul

0 Anthony Monti 9 months ago in reply to PaulM

Paul,

I'll go with the 16 and see how it works. Although, that will not be until next week sometime. I appreciate the help.

Tony

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