NetBurner Community Forum

Regarding half duplex 485, how about a max13487e/max13488e which includes auto sensing of direction, would those make it a bit easier for half duplex?

Hi there, nice find... Pity they are +5V operation only. My current design is +3.3V only

If your design has 5V available and you are going to use the eTPU then these will save you a lot of extra code and IO for swithcing the transmitter on and off.

I'll look at these for the next designs though! Just need to add a +5V supply next time as they don't have these in +3.3V.

Dave...

My idea of trying the following does not work.

while (eTPU->chan[TX_CHANNEL].scr.b.cis == 0)
{
/* wait for data to transmit */
}

It is ZERO on entry and there is still bytes going out of the serial port so my TX disable of the RS485 driver was

If I delay the TX being disabled after transmitting I get the data back from the Modbus driver but as the reply can be any length, this delay method is not ideal and I want to simply switch from TX to RX after the last byte has been transmitted.

I need to look through all the code and documents for the eTPU and see how to detect when the buffer is empty.

I think the auto enabled RS485 drivers you found will avoid this issue for you.

Cheers,
Dave...

Btw, here is some calculations for eTPU on how many uarts (and baudrate) that can be access at the same time...

http://www.freescale.com/files/training ... E_ETPU.pdf

Cheers

Nice find. Looks like my next project with 8 eTPU UARTs running at a max of 19200 each is going to work just fine.

Cheers,
Dave...

Hey RG, I got the half duplex code working. I use a PC application called Simply Modbus Master to test it and using the following code after sending via the eTPU.

With this I can detect the buffer being empty and then switch back to receive. No lost bytes

while(! eTPURec[eTPUchannel].FIFO.Empty());

eTPUchannel is the channel for the transmit line.

After this I then have a small delay based on 1.5 bit times before I disable the TX driver and it works very well.

Dave...

Very cool. I am assuming you use a hw timer, probbaly the PIT to do the delay? If so, do you use a separate PIT timer for each '485 channel so each channel can run independently? I doubt you'd want to stack up the channels to share one timer...?

Yes, I am using a PIT for the timing. I have only gotten the Modbus slave port to work and next I will do the Modbus Master next. I am therefore only using a single timer for now. As I have a common Modbus library I am looking at how to have it use a different timer.

As the speeds can be different on both Modbus ports, I am going to need a different timer for each one.

Tomorrow I will complete the code to do the Modbus master and fingers crossed it will work without any issues.

Cheers,
Dave...