Combining i2c lines with programming pins what about the pullup?

[TimB]

Hi All

Just a check before I start hacking my dev board.

I currently have a board which just needs a 4 pin connector for +5v SDA SCL and Grnd. However to program it I need the 5pins for MCLR etc. The board is small and the ICSP at 2.54 pitch is taking up nearly all of one side. What I would like to do is drop the ICSP connector and tie the Clck and Data lines to the SDA and SCL pins then all I need is a flying wire to a single pin (MCLR) and I can use a custom cable to program the board.

My question is will the 4k7 pullup I'm using cause an issue. The research I have done I get no issues or the programmer uses 4k7 pulldowns to get 0v so will be an issue with 4k7 against my i2c pullups

If the programmer drives the pins directly then they should have no issues with a 4k7 on the line.

Anybody have any thoughts?

Thanks

Tim

[trastikata]

Anybody have any thoughts?

Hi TimB,

If you think about the ICSP port, VCC and GND pins already exist somewhere on the board, so you need only 3 pins - Data, Clock and VPP, in small boards I usually place 3x 50th (1.27mm) pin headers or simply 3 small SMT soldering pads where I solder the 50th header or programming wires.

[Frizie]

Depends on what package your PIC have.
If you have a DIP or SOIC package, you can think of a test clip to which you have soldered the 5 wires.
You place the clip over the PIC, program the PIC and remove the clip.
No connector needed... 



On the picture hereabove, a 8-pin DIP test-clip is placed over a 14-pin PIC.
The five PGM connections (GND, V+, PGC, PGD and Vpp) are on the top of the PIC, so an 8-pin test clip will suffice.

[tumbleweed]

To answer your original question, the ICSP has 4.7k pulldowns and won't like pullups being added to the clock and data lines.

[TimB]

Thanks all

I was just about going to write I could pullup up the SDA SLC lines using a spare pin on the pic when it dawned on me. The Pullups are on the master board not the slave!!!    Dooow

Problem solved I think.

Tim