Electronic – ARM NXP LPC1114 current sink source capabilities

The STR91x family of microcontrollers has very flexible peripherals. Unfortunately, this flexibility makes them somewhat complicated to set up. My suggestion is to start by downloading the STR91xFA Firmware Library from ST.com. Once you have the library linked into your project, you need to do something similar to the following:

void InitGPIO7( void )
{
   GPIO_InitTypeDef GPIO_InitStructure;

   /* Enable the GPIO7 clock */
   SCU_APBPeriphClockConfig(__GPIO7, ENABLE);

   /* Initialize the GPIO port */
   GPIO_DeInit(GPIO7);

   /* Configure pin GPIO7.3 */
   GPIO_InitStructure.GPIO_Direction = GPIO_PinOutput;
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
   GPIO_InitStructure.GPIO_Type = GPIO_Type_PushPull;
   GPIO_InitStructure.GPIO_IPConnected = GPIO_IPConnected_Disable;
   GPIO_InitStructure.GPIO_Alternate = GPIO_OutputAlt1;
   GPIO_Init (GPIO7, &GPIO_InitStructure);
}

Note that this is untested but it should be pretty close.

I really don't believe that information is missing the datasheets. I have never seen it NOT there, although I have never used the particular microcontrollers you mention.

In general, at least for the micros I have used, I/O lines wake up to be as benign to the external circuit as possible. This means going to high impedance to the extent possible. In addition, pins that can be analog inputs are usually configured that way on power up. That is because digital inputs often are not intended to be held at intermediate voltages for extended time. Some might consume more power in that case, or oscillate, or do other annoying and possibly out of spec things.

However, the definative answer is in the datasheet of whatever micro you are using.