Hi there all - Will cross post this at Silabs....

I have a Silabs f047 device, with no external pullups on any of the ports.

I am using P2 as a device address with DIP switches to ground, when the DIP switch is closed.

P1 is spare and goes out to a 5x2 pin header.

P3 drives 3 LEDs and an enable line for a H-Bridge Motor driver

P0 has a PWM output and a few inputs, (TACT switches and Reed switches) as well as another enable line for the H-Bridge.

All is rosy (fine) when the DIP switch is grounded. When more than 2 or 3 of the switches are open nothing works - the motor will not operate, and the TACT and reed switches are incorrectly interpreted.


I was assuming that the internal pullups would still be operational and would pull the open inputs whether this is a TACT, DIP or reed switch to a "logic 1" hence no external pullups have been fitted.

However on carefully reading the datasheet (page 206 section 17.1.2) it states. "In the open drain configuration, writing a logic 0 to the associated bit in the port data register will cause the port pin to be driven to ground , and a logic 1 will cause the port pin to assume a HIGH IMPEDENCE state"

Hmmm - I thought to myself, does this then mean that I need external pullups on all inputs, if I want to clamp them at a known input level?

Is this why having the DIP switches open (ie HiZ) causes the other HiZ inputs to get messed up? Ie when I press the Open Tact Switch, the close button code gets run instead.

It is driving me nuts, Is there a more definitive way of ensuring that the pins used as inputs are held high by way of the internal pullups? (about 100k according to the datasheet)

Should I have external pullups on all inputs when using this chip in the future.

Also by the way I found an app-note (AN101) from silabs that said this:


"Unlike the standard 8051, true push-pull outputs are provided. If the 'strong-then-weak' pull-up function of the 8051 is required, it can be emulated in software by configuring the associated port output as 'push-pull' followed by a configuration to 'open-drain' "

Is this what will solve my woes? I tried it on the DIP to no avail. but am a little wary as the data sheet indicates that the push-pull configuration is connected directly to VDD, so having the DIP closed (to ground) means lots of current through that port.....poof


Here is my port config - sorry it is messy I have been trying to figure this out.

    SFRPAGE   = CONFIG_PAGE;


    P0MDOUT   = 0x31;
    P1MDOUT   = 0x07;					//no point configuring this it is spare
//    P1MDOUT   = 0xFF;					//no point configuring this it is spare


	P2MDIN    = 0xFF;					//this is the default for Open drain inputs
	P2MDOUT   = 0x00;					//this is the default for Open drain inputs
	P2 		  = 0xFF;					//write ones to the port to ensure it is an input

    P3MDOUT   = 0x0F;
    XBR0      = 0x14;					//PCA 0 & 1 to port pins, UART0 to port pins
    //XBR1      = 0x14;					//Int0 & Int1 to port pins
    XBR3      = 0x80;					//CAN is push pull
    XBR2      = 0x44;					//uart 1 to port pins, enable XBAR

Thanks for any thoughts, I hope I have given enough detail, please let me know if you require anything further.


Regards

Marshall Brown