LPC 55S16 | Controller Reset Problem

[Dhaya]

Here a PIN has been configured as OUTPUT. We try to give 3.3V externally to that configured PIN. It leads to controller freeze or reset problem. Kindly give the points to avoid this problem. This problem not happens in LPC 1788, LPC 1768.

This happens while developing application for the matrix keypad

[xiangjun_rong]

Hi,

It is incorrect to connect 3.3V to a GPIO pin directly which is configured as GPIO, the case should be avoided.

If you do need to connect a 3.3V to a GPIO output pin, you can connect a serial resistor, for example, the maximum  output pin source/sink current is 4mA, so you can connect at least 3.3V/4mA=0.825K ohm resistor, so you can connect 1K or above serial resistor between the GPIO pin and 3.3V.

Secondly, you can configure the GPIO pin in open drain mode, connect the GPIO output pin to 3.3V via a pull-up resistor.

Anyway, it is not recommended to connect 3.3V to GPIO pin directly without any load, which can damage the I/O cell.

Hope it can help you

BR

XiangJun Rong

[Dhaya]

Thanks for the support. But we already tried with series resistor of 1KOhm but the problem still happens in our customized board.

But in EVK this problem does not happens that's why we confused a lot why it happens only in our customized board

[xiangjun_rong]

Hi,

Can you post the related part of schematics so that we can have a review?

BR

XiangJun Rong

[Dhaya]

Here is our customized board schematic

[xiangjun_rong]

Hi,

If you change the serial resistor as 10K ohm for the R67, R68, R69, does the Resetting or freezing happen or not?

I am not clear about the SC1, SC2 and SC3 nodes, are the SC1/SC2 and SC3 driven only by P0_23,P0_24 and P0_25 or by external source?

BR

XiangJun Rong

[Dhaya]

Thanks for reply .

Yes, even if the resistor value changed to 10KOhm freeze problem was happened.

SC1, SC2, SC3 is nothing but the column control of matrix keypad. These three are driven only by the P0_23, P0_24, P0_25 (which are configured as output). There is no external sources for these PINS

[xiangjun_rong · Accepted solution]

Hi,

If you change the serial resistor to 10K ohm, the Resetting or hanging issue still exist, I do not think the two output pins connection is the cause, you have to consider the other cause.

1)pls check the power supply pins, confirm they are connected correctly.

2)check if the chip start up correctly, you can use the CTimer or systick module to generate interrupt, in the ISR, you can toggle a LED

3)PIO0_5 must be high during/after Reset so that the chip can start up and run from flash.

Hope it can help you

BR

XiangJun Rong

[Dhaya]

Thanks for help. It is solved by tried the methods you given.

By include the resistor value 10K on both SC and RET PINS, it not get into freeze/Reset mode .It becomes works in ideal state