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michael , 09-12-2024, 06:58 AM

Hi everyone, I am currently doing a DDR3 Layout. For the ADDR/CMD/CTRL-Bus I'm using xSignals because this Bus has serial termination resistors, which are set up as resistor arrays. Do I nedd to add the pin package length to these arrays or is the lenght of the package automatically calculated by the tool because it's a resistor ? I can only find information about adding pin package length to IC's but not adding them to resistors.

Cheers Michael

QDrives , 09-12-2024, 07:39 PM

Can you show a screenshot where it is shown that you cannot add it?

michael , 09-13-2024, 06:22 AM

I'm sorry if I made myself unclear. I was wondering if it's necessary to add the Pin Package length to a resistor array. Because when it comes to this topic, it's always referred to as the bonding wire length inside an IC. I never read anything about resistors. Of course I can add it to the array pins.

Robert Feranec , 09-13-2024, 08:47 AM

Do you really need termination resistors in xSignals? Also, if length matching is needed for signals with series termination resistors, add them on all the lines, this will eliminate need of considering them for length matching.

michael , 09-13-2024, 11:51 AM

Hi Robert, thanks for chiming in. That's funny, I asked the same question about the resistors. As far as I understand, the controller (MCU) is not able to adjust to the required line impedance by internal resistors, and that's the reason for the external arrays. In fact these arrays are added to all the lines of ADDR/CMD/CTRL, except the clock. Which now should be a little bit too short. Referring to the design guide of this MCU, DDR_CLK should be 0-1mm longer than the rest of the ADDR/CMD/CTRL-bus. So I think, if I understood you correctly, I need to consider the resistors for length matching.

Robert Feranec , 09-14-2024, 04:21 AM

I understand now. Interesting. I would probably add 0R into clock. How they did that on reference board?

michael , 09-17-2024, 08:12 AM

On the reference board they placed 56R (Pullup) to VTT_DDR at the end of each line. These resistors are placed "around" the DRAM, even though they're on the opposite side. This creates quite long stubs that would not have been necessary, as they could have been placed much closer to the vias on the opposite side. It's a bit weird. This board also has an interposer between MCU and DRAM. Btw, it's the STM32MP15x-EVAL board.