I/O pins

[chandu13]

Hay

What is the status of the I/O pins of the LPC2114 when the controllers RESET
According to the data sheet when controller Resets the I/O pins act as the Inputs and status of the pins is Undefined.
Voltages across the pins are 3.3V, 2.1v, and 0.1V when controller reset
Please give some information regarding the I/O port internal structure

Regards
chandu

 

[futz]

What is the status of the I/O pins of the LPC2114 when the controllers RESET
According to the data sheet when controller Resets the I/O pins act as the Inputs and status of the pins is Undefined.
Voltages across the pins are 3.3V, 2.1v, and 0.1V when controller reset
Please give some information regarding the I/O port internal structure

As you said, on reset the pins are set as GPIO and as inputs. What else do you need to know? That's the safest mode for them to default to. Your program takes over from there and sets them how you want.

I'm just now learning ARM7 with the Olimex LPC-P2148 board.

**broken link removed**

I assume you've been to this page and clicked on the "Download all documentation" link, right?

 

[chandu13]

Floating voltage

Hay

I have interfaced LEDs with LPC2114 using 74LS244 buffer
I am making port pin high (1) LED is glowing
I am making port pin low (0) LED is not glowing
But whenever I reset the controller the controller pins act as the inputs, at that time the voltage on the pins is floating
74LS244 buffer input reading floating voltage as the high & LEDs are glowing when the controller is RESET.
How to solve the problem & please provide some information regarding the interfacing.


Regards
chandu

 

[futz]

I have interfaced LEDs with LPC2114 using 74LS244 buffer
I am making port pin high (1) LED is glowing
I am making port pin low (0) LED is not glowing
But whenever I reset the controller the controller pins act as the inputs, at that time the voltage on the pins is floating
74LS244 buffer input reading floating voltage as the high & LEDs are glowing when the controller is RESET.
How to solve the problem & please provide some information regarding the interfacing.

Your program is not restarting after reset. Mine does the same thing. I still don't know enough yet to fix that. I know it's not terribly difficult, and I have some vague ideas about how it's done, but I'm still a bit of a newb on ARMs. The second I know how it's done I'll post it here - if you learn it first, you post.

What I do as a workaround for now is fire up the debugger and re-run the program again from there.

 

[Leftyretro]

Most microcontrollers set their I/O pins as inputs by default after power-up or reset. If you need a signal to stay high or low during a reset cycle then a simple pull-up or pull-down resistor should work.

Lefty

 

[chandu13]

Pull Down

Thank for the reply

In my case I have to use PULL DOWN resister
LPC2114 source & sink current is 5mA &V=3.3v, for how much ground current is needed for pull down
Please suggest How to calculate the pull down resister

Regards
chandu

 

[Arkham00]

Pull down resistor

From a 74LS244 datasheet I see "input low current" as low as 0.2mA for input at 0.4V so the resistor should be about 2kohm but the pin of your microcontroller may have a pull-up resistor inside. Check it and, if it's your case, use a lower pull-down resistor. I think that a value from 1Kohm to 2.2kohm should be fine in your project.
I you use a 74HC244 buffer, instead of the LS one, you may use much higher resistor (10kohm to 100kohm) and reduce current consumption.