RS232 FLOAT_HIGH? [Confirmed as bug by CCS...]

hmmpic · Joined: 09 Mar 2010 Posts: 314 Location: Denmark

[Update. CCS confirmed it as a bug, fixed in next release they say.]

Need my software RS232 to go Low, and Float, NO High.

From CCS:
FLOAT_HIGH - The line is not driven high. This is used for open collector outputs. Bit 6 in RS232_ERRORS is set if the pin is not high at the end of the bit time.

CCS 5.105 & 5066

Then i see this

03D58: BCF TRISC.3 -> Output
03D5A: BSF LATC.3 ->Go High

temtronic · Posted: Tue Mar 15, 2022 5:37 am

You should post which PIC, the pin may not be able to be FLOATed either physically or as a 'software UART' ??

hmmpic · Joined: 09 Mar 2010 Posts: 314 Location: Denmark

18F26K22

Look at this:

temtronic · Posted: Tue Mar 15, 2022 6:55 am

hmm, wondering if you have to disable the other peripherals 'attached' to that pin like the ADC or MSSP ??
I'm sure others KNOW for sure....

hmmpic · Joined: 09 Mar 2010 Posts: 314 Location: Denmark

Nop, it is CCS startup-code for the RS232. Nothing i can do.
#useRS232(Baud=1200,PARITY=N,XMIT=PIN_c3,BITS=8,TIMEOUT=10,STREAM=pdebug,ERRORS,FORCE_SW,DISABLE_INTS,INVERT,FLOAT_HIGH) //software com for production test on the IR led.

I suggest CCS made a new param for the useRS232. Call it "SIMPLE_FLOAT" no check and all that stuff, just float.

temtronic · Posted: Tue Mar 15, 2022 8:13 am

even better, an 'option=just_work'
where it magically figures out everything needed to work as you need it to Smile

Ttelmah · Joined: 11 Mar 2010 Posts: 19500

As always the big problem is lots of PIC's with different abilities.

FLOAT_HIGH historically only worked on software RS232. The manual entry
saying this was removed when some of the newer PICs, offered
programmable open collector drives on pins.
This PIC is not one offering this. CCS on these 'assume' a traditional
PIC where the pin can still be driven by turning off the TRIS. Unfortunately
on most of the mid-aqe PIC's, when a peripheral is enabled, this overrides
the TRIS.

So currently FLOAT_HIGH will only work on:
Software serial.
New PIC's with open collector drives.
Old PIC's where the TRIS has to be set for the serial to work.

hmmpic · Joined: 09 Mar 2010 Posts: 314 Location: Denmark

Maybe see my first post:-)
#useRS232(Baud=1200,PARITY=N,XMIT=PIN_c3,BITS=8,TIMEOUT=10,STREAM=pdebug,ERRORS,FORCE_SW,DISABLE_INTS,INVERT)

Only thing i miss is the floating pin, not high. It is not related to any hardware it is pure software. And this function is missing in the software uart.

I solved it in my hardware with a diode:-)

Ttelmah · Joined: 11 Mar 2010 Posts: 19500

I'd be very surprised if 'float_high' will work with 'invert'.
With invert, the default idle state is low, not high.....
Also understand the key part of the word 'FLOAT'. The line is undriven.
It'll only go high if you have a pull up resistor on it.
The point is that the 'idle' state between the bytes is done by turning the
drive off, so the line floats. With invert the compiler can't understand what
is wanted.

Simplest thing is just immediately after each byte is output set the pin to
float. So:

hmmpic · Joined: 09 Mar 2010 Posts: 314 Location: Denmark

[Update. CCS confirmed it as a bug, fixed in next release they say.]

I have the bug in: 5105 & 5066.

Ttelmah · Joined: 11 Mar 2010 Posts: 19500

Good.
I don't think it had 'occurred' to them, that somebody might want to use
'float_low'. So not surprised it didn't work.
Just use the proposed fix for now (this will give the same behaviour). If
you set the call up to with a macro, you can then switch to the fixed
code with a one line change. Smile