UART1 RTS in 485 mode

[tarik]

I'm trying to use my MOD5234 board's UART1 for controlling a 485 transceiver but can't get any signal from the RTS line. I open UART1, then call Serial485HalfDupMode(1,1), but don't get the expected behavior from J2[23] (UART1 RTS). I've also tried calling J2[23].function( PINJ2_23_U1RTS ) before and after the Serial485HalfDupMode() call with no results.

I'm controlling another RS485 transceiver from UART0 and had no problems - I call Serial485HalfDupMode(0,1) and this sets up J2[38] to act as the UART0 RTS signal as expected

Any advice or working sample code would be greatly appreciated.

Thanks,
Tarik

[Ridgeglider]

I asked Larry essentially the same question recently. Most of the dev. boards are set up to only support 485 on Com0, but you can modify this if you add your own external driver. For this reason, the NB Serial485HalfDupMode() function un-neccessarilylimits halfduplex to Com0. Be aware that (at least on the 5234) the RTS pin for Uarts1 & 2 is shared: you can only use one, not both. If you need 485 half duplex and don't want to set up an external driver, you can also swap the default serial port (usually used for stdIO) from Com0 to Com1 by going into the setup menu in the monitor. That frees up Com0 from routine stdio/debug stuff (by routing it to Com1) so you can do the 485 half duplex thing on Com0.

Here's my question and Larry's reponse:
The serial.h Serial485HalfDupMode() function looks like it would
work for all three regular (non-eTPU) UART ports: Com0, 1, and 2.
However it exits if it is passed anything but Com0. If I eliminate the
lines at the start of that function:

if ( port != 0 )
{
return;
}

it looks like it would work for one or the other of the remaining Com1
or Com2 ports, but NOT both because the *RTS/*CTS lines J2[23]=*RTS
and J2[24]=*CTS are shared between those two ports, and you can only
choose Uart1 or 2 at a given time. Is this correct?

Larry replied:
This looks like it is correct. This function should be:
if ( ( port > 2 ) || ( port < 0 ) )
instead of:
if ( port != 0 )

And yes, since the RTS signal is shared you will only be able to use port 1 OR port 2.

[tarik]

Ridgeglider:
KA-ching! That was the problem. I hope NetBurner takes note & implements this change in the system firmware builds.
Thanks!
Tarik

[lgitlitz]

These changes have already been added, they will be in the next build

-Larry