UART Problem

TargetBusy · Joined: 07 Jan 2012 Posts: 6

My first post and is a problem... oh well.

I'm new to CCS, not to microcontrollers.
But I've found a brick wall trying to figure out what is wrong here.

Just trying to make the PIC12F1840 with the UART library is impossible.
The same Header of the 12F1840.h declares:

Ttelmah · Joined: 11 Mar 2010 Posts: 19513

First try defining the pins for the UART using the #pin select function.
Then, in the #use RS232 use 'UART1', rather than the pin numbers. This way the code is generated to talk to the hardware UART.
This should setup the pin mapping, and then generate the code to talk to the UART.
Make sure you turn off the ADC on these pins - the ADC overrides the UART.

However haven't tested with the 1840 (have done with some of it's earlier cousins). The 1840, is very new. CCS quite commonly has problems with getting the settings right for the first few versions with a new chip. If it doesn't work, leave the #use RS232 talking to UART1, and manually add your own settings for the APFCON register, with code like:

TargetBusy · Joined: 07 Jan 2012 Posts: 6

Thank you Ttelmah,
Worth the effort but I'm in square zero again. It didn't work.

The fact that this PIC has its own EUSART module is the clue that this feature works in a different way than using UART defines.

Is hard to debug something when there is no examples codes around. I guess that I jumped to this PIC too early and I'm not that good on assembly anyway.

I only hope to find something around or at least that someone will post a working code on this thread some day.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Post your compiler version, because as Ttelmah said, there may be
problems in your version. The version is a 4 digit number, like 4.128, etc,
and it's given at the top of the .LST file, which will be in your project
directory after a successful compilation.

TargetBusy · Joined: 07 Jan 2012 Posts: 6

Ttelmah · Joined: 11 Mar 2010 Posts: 19513

Seriously, I don't see anywhere in the code you post, where you are trying what I suggested!....
I suspect you have misunderstood slightly, switching to a stream, rather than telling the compiler to use the UART.

The problem is that A0, and A1, are _not_ automatically the hardware UART pins.
Your #use RS232 needs to use:

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Hopefully to help a bit.
A pic can have more than one hardware uart and then there are always software uarts. Stream is useful when there is more than one uart since it names each uart configuration and in conjuction with fprintf your output can be directed to the appropriate uart. Now UART1 ..UART2 identify the hardware uart. Sure you could specify the pins by why bother the compiler when it sees UART1 will use the hardware pins for that specific device. For the software uart you have to specify the pins to the compiler. Some PIC's allow for the hardware ports to be remapped. This is where pin select comes in....it allows you to choose another pin than the default pin for the uart.
Not all pins are remappable so check the PIC device spec sheet. The compiler will error the pin select if you choose a non remappable pin but it is still best to check the specs. Oh and notice how Ttelmah added ERRORS this is very useful ( it allows the uart to continue after an error occurs) since it can avoid head scratching if the uart hangs glitches.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I tested all four combinations of the Tx/Rx pins on the 12F1840, and
the compiler generated a software UART for all of them. I also tried
using "UART1" instead of specifying the pins. It still made a soft UART.
This is with vs. 4.128.

Work-around code can be done, but how important is it to you to use a
H/W UART on this PIC, right now ?

TargetBusy · Joined: 07 Jan 2012 Posts: 6

TargetBusy · Joined: 07 Jan 2012 Posts: 6

Update on the troubleshooting to Ttelmah's suggestions.

This code:

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I just don't think CCS has it all working on the 12F1840. If you have
4.128, and you recently bought it, then you should be able to ask CCS to
add hardware UART support, and #pin select support in the next version.

Here's an example of how to add support with code, but why bother,
if you can get CCS do it all for you in the next release ?
http://www.ccsinfo.com/forum/viewtopic.php?t=26631&start=8

TargetBusy · Joined: 07 Jan 2012 Posts: 6

Mike · Joined: 16 Jul 2009 Posts: 4

Guys,
Thanks for the post. I "wasted" 5+ hours on this UART until Google discovered your posts. Thanks it was very helpful.

I upgraded from v4.109 of the compiler where FORCE_SW seemed to work but delay_ms() was broken. I can take the same code and compile for PIC12F675 and put in place of the PIC12F1822 and it works. However for v4.128 the following doesn't work at all!

There is no TX output for any of the following serial port definitions:

RF_Developer · Joined: 07 Feb 2011 Posts: 839

There is only one UART on this PIC, but it can work through either of two pairs of IO pins. UART1 selects the first, default pair, UART2 selects the second pair. You must have your serial hardware wired to the second pair: RA4 & RA5. UART1, the default, selects RA0 & 1.

If you force AFPCON by writing to it after setting up the UART then that may or may not have the effect you are expecting as you are implementing a software UART, which is not steered by AFPCON, just the availability of the relevant IO pins.

If you specify a timeout that will force a software UART as the hardware UART doesn't have that functionality.

RF Developer

Mike · Joined: 16 Jul 2009 Posts: 4

Sure. I as I stated in the post it has only one UART, but the PU/reset value of APFCON is 0, which from the datasheet maps TXD to RA0, see Register 12-1. I'm saying is that UART1 doesn't select the default pin assignments for TXD.

Sure it makes some sense to have UART1 and UART2 specify the different default configurations but RXD and TXD can be individually assigned. Regardless, setting UART1 or UART2 should access the same SFR's to control the sole UART and setting APFCON.2 to 1 (TXCKSEL) still doesn't fix it when UART1 is selected. What I mean is by d-scope monitoring on both RA0 and RA4 there is no activity when UART1 is selected. It seems with UART2 you can then select which pin has TXD activity. Which means it is UART code is broken with UART1 selected.

For me FORCE_SW option didn't work on the 12F1822 at all. It did on my previous version 4.109 and it worked with a 12F675 but I upgraded yesterday to 4.128 and then it was broken on the 12F1822 but not on 12F675. I would say it is a compiler or library issue.

I don't think you are correct about the timeout option, see page 141 of 7-14-2011 PCB-PCWH compiler manual and CCS F1 help file. Also, there is a 34 instruction word difference btw compiling w. and w/o FORCE_SW.

Thanks.