Interfacing OMAP-L138 uPP for 1/2 duplex ADC and DAC operation

William Leigh

Other Parts Discussed in Thread: OMAP-L138, OMAPL138

Hello:

I've been poring over the datasheet sprugj5b.pdf "TMS320C674x/OMAP-L1x Processor Universal Parallel Port (uPP) User's Guide" (see page 12) and

SPRS586B.pdf "OMAP-L138 Low-Power Applications Processor" datasheet (page 243)

to find a way to configure the uPP to

1) transfer data out to a DAC under DMA control, including 16-bit parallel data and clock OUTPUT, then

2) switching the interface to transfer data in from an ADC under DMA control, including 16-bit parallel data and clock OUTPUT to the ADC.

From the text of the uPP User's Guide (page 12) , it appears that the CLOCK pin for the uPP in receive mode is an input only, while what I require is a clock output to drive the ADC which is synchronous with the START and ENABLE pins presumably provided by the uPP DMA channel.

Is there a way, without external logic, to generate this RECEIVE clock..?

Thanks,

- Bill

over 14 years ago

0 Zhengting He over 14 years ago

TI__Intellectual 1380 points

Bill,

The clock for the input channel is input only. I don't see how to achieve the functionality without external logic.

0 AndyH over 14 years ago

Prodigy 30 points

Bill,

The clock pin for the UPP in RX mode is, as you said, an input. I don't know if your architecture will permit it but you can use the ePWM / eCAP peripherals which also allow you to synchronise the START / ENABLE pins.

Andy Harris

AGD Systems Limited

0 Peter Simpson over 13 years ago in reply to AndyH

Prodigy 10 points

I'm working on a design which will need to read from four ADCs. I'll be multiplexing their outputs onto the UPP input pins, and providing a clock pulse for each data word. However, the ADCs acquire and convert simultaneously, so there will be a period where no clock pulses are generated. Does the OMAPL138 require a continuous clock on the uPP clock pin, or can it be discontinuous?

0 Saravanan Karivandan over 13 years ago in reply to Peter Simpson

Prodigy 10 points

Hi,

We are also facing same kind of problem where we need to collects samples from two asynchronous ADC's(Analog device make AD7656) using UPP of OMAP-L138.

Let me know the solution if you find. Please update me on the below mail ID.

saravanan.k@easunreyrolle.com

Thanks for your valuable help.

Regards,

Saravanan.K

0 yanbin xing over 13 years ago in reply to Saravanan Karivandan

Prodigy 170 points

How about using a McBSP to drive uPP clk&start.

Just need to start a McBSP DMA, and only a little system bandwidth consume.

If this way works, please let me know.

0 Joe Coombs over 13 years ago in reply to yanbin xing

TI__Expert 8890 points

We have recently published a whitepaper describing one way to interface a DAC and ADC with the uPP peripheral. You can find the document at the following location:

http://www.ti.com/lit/wp/sphy007a/sphy007a.pdf

This is by no means the only solution, but it should be a useful example or starting point.

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Interfacing OMAP-L138 uPP for 1/2 duplex ADC and DAC operation