Olimex PIC-P40-USB Proto Development Board

lrysavy · Joined: 30 Nov 2006 Posts: 4

I am using a Olimex PIC-P40-USB development board with a 16F877A pic. I am trying to use my laptop computer with a PCMCIA RS232 serial port card in the slot to communicate with the CCS bootloader loaded in the pic. The board is being powered off the USB cable and is on com port #6. I have the 9 pin UART on the Olimex board connected to the PMCIA card on com #1. For a terminal program, I am using the CCS terminal program ship with my compiler which is set to com 1, 8N1. The problem is that I can not get the board to talk to the PC. I keep getting a time out error. For a test I hooked a 16F877A pic board with a MAX232 to the com port on the laptop and it works fine. Any Ideas?

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

Couple of observations
Laptops often don't provide much power to the USB
Laptops often don't provide enough voltage to the RS232 port

Assuming all works with a desktop PC then for the laptop:

If you have a powered usb hub then try putting it in the loop laptop to hub hub to your board.
Scope the laptop RS232 to see what kind of voltage swing you are getting.

Ttelmah · Guest

Why use the PCMCIA card?. You already have a USB serial port built onto the P40 board. If you use an external serial, this will need a MAX232 chip or similar, to make the signals compatible with the PIC. At the moment, it sounds as if you have got the USB serialport 'looped back' to the PCMCIA port. In which case, it is not suprising that you can't talk to the PIC...

Best Wishes

lrysavy · Joined: 30 Nov 2006 Posts: 4

Ttelmah · Guest

It already is.
A 'comm port', provides no power. The USB connection provides power, and attached to it isa circuit that produces a 'virtual' comm port, Your serial connection is reliant on the power already coming from the USB connection.
The serial port available from the FTDI module, is signalling at TTL levels (which will be compatible with the PIC), while the one from the PCMCIA card, will be signalling at RS232 levels, and will require a level shifter chip (MAX232), which will draw more power...

Best Wishes

lrysavy · Joined: 30 Nov 2006 Posts: 4

Ttelmah · Guest

You can't just plug in, and expect to connect. You need to make the wiring connection between the FTDI circuit, and the PIC. You need the 'TX' pin of the FTDI circuit, attached to the 'RX' pin on the PIC, and the 'RX' pin on the FTDI circuit connected to the 'TX' pin on the PIC. Circuitry is not automatically connected. The 'point' about the board, is that it is laid out so that you can connect stuff as you want, but because of this, there is no 'default' interconnection...

Best Wishes

lrysavy · Joined: 30 Nov 2006 Posts: 4

Ttelmah · Guest

It is not clear.
RXD, may have a connection, but it is not 'plain' that it does, but no connection is really shown to the PIC's TXD pin. However the diagram is so poor, that a connection may exist (try testing with a meter).
The 'standard' in circuits, is that if a pin has a 'node' shown, and the node is named, then they should be connected. However no node is shown on either pin.just unconnected 'lines'...
No. read what I already posted. The FTDI module gives 5v 'logic level' serial, so does not need a MAX232.

Best Wishes