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McASP using TDM with multiple devices and generating a transceiver enable output

Nick Langford
Prodigy 70 points
Other Parts Discussed in Thread: AM1705, AM1707

Hi,

We are designing a multi-channel audio system using the AM1705 processor. There will be multiple AM1705 processors on the same TDM bus. In the manual section 23.2.3.4  and 23.2.4.2.2.1 it talks about having multiple CPUs on the same TDM bus and configuring the device to be active or inactive during a TDM slot. So this would work with the devices directly connected.

Due to the construction of our system we are using MLVDS at the physical layer to interconnect the CPUs, for noise immunity and to lower emissions, etc.

My question is; is it possible to get the device to generate an enable output which corresponds with the TDM slot transmission so that the transceiver direction is correctly selected. There is one way I can see, by using a second serialiser loaded with the same slot information and all '0's or '1's and allowing the high impedance state of that serialiser to change the state of the first. This is a little worrying as the high impedance state will have a slower transition time that an actively driven output. So I am hoping for a more direct mechanism.

Regards and thanks in advance.

  • 0
    TI__Guru**** 393215 points
    Moving this to the AM1X forum.
  • 0
    TI__Mastermind 35645 points

    Hi,

    Thanks for your post.

    In my opinion, the McASP receiver of AM1707 device also supports a 384 time slot TDM mode (DIR mode), to support S/PDIF, AES-3,

    IEC-60958 receiver ICs whose natural block corresponds to McASP frame size of 384 samples, but i don't think, it supports multipoint LVDS standard transceiver for the device to generate an enable output.   I do think, Texas Instruments M-LVDS portfolio provides devices covering signal rates from 100-250. Table 2, section 4 of app. report below summarizes the portfolio, the data sheets for each of these parts can be found online at www.ti.com/interface.

    http://www.ti.com/lit/an/slla108a/slla108a.pdf

    Few parts on the SN65MLVD200 Series with the above portfolio covers transceiver functionality and kindly check it. Also, receiver specification like input impedance and leakage current on a multi-point environment are mentioned in the above app. report section 3.2, please check that too.

    Thanks & regards,

    Sivaraj k

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  • 0 in reply to Sivaraj Kuppuraj
    Prodigy 70 points

    Thanks for the reply. Without any further input I will have to assume "no", then?

    Is it possible to have the McASP to easily loop (repeat) the current value? That would allow using another serialiser  transmitter output to control the enable without continuously reloading the output. You could of course do that use DMA, but this would add unnecessary overhead.