Port C High-Z...really?

[dpcons]

I thought that Port C data lines came up in High-Z mode till I got around to setting DDR and output registers. It doesn't appear that this is the case. I'm trying to force bit 15 of port c low after reset (before and during the NB 2 sec startup delay) using a 10K pulldown and also bit 14 high using a 10K pullup. Bit 14 pulls up successfully but bit 15 appears to remain at High-Z until the 2 sec startup delay is done and the code sets the I/O port ddr and data register. Anybody know what's going on.

[lgitlitz]

Hi,

What processor are you using? It sounds like the MCF5272. This processor is strange in the fact that after reset it has pull-up resistors on all GPIO signals until the ddr register is written... from the MCF5272UM:
"To avoid indeterminate read values and reduce power consumption, internal pull-up resistors are active immediately upon reset, and remain active until the corresponding port direction registers are programmed."

Since the pin you are trying to pull-down appears to be in hiz, I bet they are using close to 10K for the internal pull-up resistors. Try using a 1K or 2K pull down instead.

-Larry

[rnixon]

Tough to answer without knowing what processor/platform you are using.