Serial comms / Bootloader

[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 ">