I'm new to micros and I've been following the HKRMicro course; however, I'm using a Cygnal C8051F005 kit. Each I/O can be configured as open-drain or push-pull. Then all the I/O's configured as open-drain can have an pull-up enabled or disabled. I think open-drain with pu work the same as the push-pull except the pull-up resistance values are different (~120k for open-drain and below 150 for push-pull).

I configued all the I/O as open-drain with pu and the LCD data lines to P3 and control lines to 3 bits of P2. The LCD didn't work, but when I started single stepping through the program it did. I did some reading and assumed that the 120k pull-up resistance was to large and wouldn't let the lines change states fast enough. So I then configured all ports as open-drain without pu and added an external 10k resitance and it worked fine. I suppose that the internal 120k resistance was too large?????

I measured the current on the push-pull used as an input and when it is connected to ground about 19mA flows. This doesn't sound very desireable???? So this means if I want setup other inputs I have to add an external resistor. Thats no big deal, but it doesnt seem really ideal either. Does my analysis on all this sound correct???