Serial comms / Bootloader

[koossa]

Good day

I have setup my circuit to be able to do serial comms as well as bootloader software as described at this thread:
http://www.picbasic.co.uk/forum/show...ght=bootloader

And have used Mister_e's code here:
http://www.picbasic.co.uk/forum/show...1&postcount=11

But everytime I connect or disconnect using hyperterminal it switch my pic off?
Any idea why this happens?

[mister_e]

Probe your MCLR pin when you disconnect the RS232 cable.

What's happen? Should go to GND for XYZ time. Place a pull-down resistor on pin 8 of your MAX232.

[koossa]

Hi Steve

Thx
I don't have instrumentation to do a probe on mclr.
Must I just put a pull down resistor on the max (What size 2k)?

[mister_e]

let's say <10K should be enough. Also... be sure MCLR is tie to VCC with pull-up too.

[mister_e]

a simple probe... use another PIC.

Start:
    While PICInput=1 : wend
    HIGH LED
    pause 2000
    LOW LED
    goto Start

[koossa]

Thank you!

[koossa]

Hi Steve

Someone told me that the MAX232 has an internal 5K pull down.
It would not be necessary to put a pull down resistor as you have described.

Is this correct?

[mister_e]

If i refer to the Maxim datasheet...
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=573&stc=1&d=1130593189 ">

there's indeed a pull-down resistor... mmm for the TI one, i guess it's the same.

mmm... Hyperterminal could be the cause...

1. did you disable the handshaking?
2. What about if you use MicroCode Studio Serial Communicator instead?
3. Is your MCLR pin is tied to VCC via resistor?
4. What about if you use the original solution (resistor instead of capacitor)?

I bet on the Handshake idea now.

[koossa]

-did you disable the handshaking?
<font color="red">Yes</font>
- What about if you use MicroCode Studio Serial Communicator instead?
<font color="red">MicroCode Studio Serial Communicator works!!!</font>
<font color="red">But with visual basic or hyperterminal it does not work?
Any idea what is the difference between the 2?
</font>
-Is your MCLR pin is tied to VCC via resistor?
<font color="red">Yes</font>

[mister_e]

In VB you'll need to disable the DTR line. Here's a usual COM port setting in VB

    '   Serial Communication Definition
    '   ===============================
        '
        With MSComm1
            .CommPort = 1                 ' Using COM1
            .Settings = "9600,N,8,1"      ' 9600 bauds, no parity, 8 data bit,
                                          ' 1 stop bit
                                          '
            .Handshaking = comNone        ' no handshaking
            .DTREnable = False            ' disable DTR line.. avoid PIC stuck if using
                                          ' bootloader circuitry
                                          '
            .EOFEnable = False            ' disable EOF event
            .InputMode = comInputModeText ' Get Text from COM port
            .RThreshold = 1               ' amount of character to be receive prior to
                                          ' generate a CommEvent
                                          '
            .InputLen = 0                 ' get the whole string
            .PortOpen = True              ' open COM port
            End With

MCS don't use and disable the DTR line for you.. not Hyperterm (wich i stay far of)

[Acetronics2]

Hi, Steve

Have a look there : http://www.beyond-designs.com/PC_ports.htm#VBHexTerm

or :

http://www.synthmodules.com/other/VBHexTerm-Setup.exe

... nice !!!

Alain

[Melanie]

Steve - Before you confuse half the forum readers - that's not a MAX232 jpg...

[mister_e]

Yes it is! comming directly from the Maxim datasheet bellow...
http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf
there's some little character to read at the bottom of the picture ;-)

From the Maxim datasheet:

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=576&stc=1&d=1130688459 ">
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=577&stc=1&d=1130688459 ">


From the Texas Instruments datasheet:

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=578&stc=1&d=1130688459 ">

[Melanie]

The correct pic is in the datasheet you just posted, but what I'm trying to say is that the jpg you've put up a couple of posts above is not of a MAX232... a MAX232 does not have enable connections on it's inverters. I refer you to Figure 5 on Page 17.

[koossa]

COOL!!

DTREnable is working!!!!
Thank you Steve!!!