Matteo Lasagni

FRDM-KW019032: misleading manual, unconnected pins, incorrect schematic, not working UART

Discussion created by Matteo Lasagni on Sep 26, 2017
Latest reply on Oct 5, 2017 by Gerardo Rodríguez

Hi, I have purchased an FRDM-KW019032 development board and I am trying to interface it to external hardware.

 

As the board is equipped with many connectors, supposedly compatible with the Arduino pinout, I started with designing the external hardware.

With big disappointment I have discovered that the majority of the pins on the external connectors is not physically connected to the MCU. According to the pin definition reported in the manual "Document Number: FRDMKW019032UG, Rev. 0, 11/2015", it appears that such pins should work straight away, out-of-the-box.

Instead, after a deep analysis of the FRDM-KW019032 schematic it turns out that many non-populated bridges (zero-ohm-resistors) are required in order to route the MCU I/O to the external pins.

 

I think that the document FRDMKW019032UG is pretty much misleading in this regards, as it does not mention that in order to use the connectors J1-J4 reported in tables 3. and 4., one must first populate all the zero-ohm-resistors indicated in the schematic as DNP (do not populate).

 

In my humble opinion, this is quite frustrating as the expectation when I bought this expensive board was to have it work out of the box as the manual indicates.

 

I believe that either the manual and the webpage must clearly state that all the external pins are not connected by default,  while it is necessary to manually solder all the missing resistors, or provide the FRDM-KW019032 board equipped with the missing resistors.

 

The schematic reports in a note that in order to source power to external pins some resistors need to be populated.

First, this note only indicates how to supply power externally but does not mention that the same action is required to have analog and digital I/O on external pins.

Second, this note is incorrect as it report wrong pin numbers. For example, where it says: "To source 3.3V to J3.10: populate R127" the pin J3.10 is wrong as the correct pin where 3.3V are sourced is J3.8. The same occurs for all the other pins reported in this note.

Another issue I have encountered (now reported to the technical support) is that the UART communication is not working on pins 2 and 4 of connector J1. The schematic indicates that a voltage-level translator is embedded on the board to match the external I/O voltage range and the MCU I/O voltage range.

Also the voltage translator (U17 on the schematic) is not powered by default but it requires a resistor (R138 according to the schematic).

After having populated the board with the missing resistors, I have connected the external UART device to the pins 2 and 4 of J1 (UART0 RX/TX) discovering that the voltage level-translator is not working properly.

Without the external device, indeed, the serial communication between the board and the PC (it works through the MK20 which is embedded on the board and exploits the same UART0 interface) works properly. As soon as an external device is connected to the external TX/RX pin nothing works. 

What is really puzzling me, is that even when I connect the high-impedance probes of an oscilloscope on the external TX/RX pins, the serial communication through the MK20 is also interdicted.

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