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Frequently asked questions
LPC2000 Family Peripherals, GPIO FAQ
- Are LPC2000 inputs/outputs true GPIOs?
- Can multiple ports be read at one time?
- Can the internal pull-up resistors on port pins be disabled?
- What are the current source/sink capabilities of the LPC2124 GPIO pins?
- What is the toggling speed of the GPIO pins?
- While debugging through code that involves Fast GPIO ports, I see that the debugger does not show the correct contents?
| Q | Are LPC2000 inputs/outputs true GPIOs? |
| A | All LPC2000 microcontroller port 0 pins are true bi-directional GPIOs. The only minor exception is that the two I2C pins have an open drain output structure. With external pull-up resistors, they can also be used as true GPIOs. The LPC210x microcontrollers don't use push-pull or open-collector output pins as found on the 80C51. When GPIO functionality is selected for the pin and it is in output mode, the LPC210x pins act as full-drive I/O pins. Internal pull-up resistors are not used to create a high-output state as they are in the 80C51. |
| Q | Can multiple ports be read at one time? |
| A | 32 I/Os can be read at a time. |
| Q | Can the internal pull-up resistors on port pins be disabled? |
| A |
In most devices, the pull-up resistors are always active.
They cannot be disabled.
Care should be taken when the chip enters power down.
If any of the port pins that have internal pull-up resistors were held low then those would typically consume around 50μA per pin.
In other devices (such as the LPC23xx and LPC24xx series), there is a register which controls the activation and deactivation of the pull-up resistors.
Software has full control over the pull-up resistors in these devices.
|
| Q | What are the current source/sink capabilities of the LPC2124 GPIO pins? |
| A | The GPIO pins can source or sink 4mA maximum. |
| Q | What is the toggling speed of the GPIO pins? |
| A |
The toggling speed on the standard GPIO pins is system_clock/14.
If 72MHz operation is used, then the toggling speed is around 5MHz.
The toggling speed on the Fast GPIO pins is system clock/4.
If 72MHz operation is used, then the toggling speed is around 18MHz.
|
| Q | While debugging through code that involves Fast GPIO ports, I see that the debugger does not show the correct contents? |
| A | This is a known issue, and most debuggers will show this behavior. Please avoid single stepping through Fast GPIO code. If you have to single step, then try keeping the memory window closed during debugging. |
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