lpc804 pull up resistor value

[yarzartunaung]

hello,

could u advise what the value of internal pull up and pull down resistor value for lpc804 is? thanks!

[BerlinRaj]

how to configure the IOCON register and how to enable the pull down in pio0-7 in  lpc804? give the example

[kangsenlu]

To configure the IOCON register, you must first find the address of the IOCON register you are modifying. After you have the address, it is simple to simply use "*addr = value;" to change it.
However, you must first enable clock to the IOCON subsystem with "LPC_SYSCON->SYSAHBCLKCTRL0 |= (UART0 | SWM | GPIO | IOCON);".
I have noticed that although the user guide says the IOCON reset value is 0xb0, i.e. pull-up resistor enabled. But my own debugging indicates that IOCON value was reset to 0. So I have to manually set that IOCON register with my code.

[kangsenlu]

After some more investigation, I found that we must turn on clock to the IOCON subsystem. Otherwise, the chip will NOT automatically set the IOCON register to the default value of 0xb0.

[nxf51211 · Accepted solution]

Hi,

The pull-up and pull-down are not passive resistors but active current sources (they typically deliver around 50µA when enabled) that is why there is not a precise value for them. Please refer to the "Ipu"/"Ipd" and "Vi" characteristics in the LPC804 data sheet (Electrical pin characteristics, located at the Table 14, page 48):

So for example, if a pin at pull-down has a typical Vi of 5V, the current would be of 50µA and therefore the internal resistor value would be of 100 KOhms.

I hope this information can help you, and please ask if you have any more doubts.

Ricardo Delsordo.

[yarzartunaung]

thanks Ricardo...