EEVblog Electronics Community Forum

Electronics => Projects, Designs, and Technical Stuff => Topic started by: Brathahn on November 28, 2020, 12:48:11 am

Title: Can't communicate with MCP39F511 power monitor via UART
Post by: Brathahn on November 28, 2020, 12:48:11 am

Hi,
im trying to communicate with an MCP39F511 power monitor IC but its not responding.
i have connected a ftdi uart/usb converter to it and the ftdi chip is sending the data correctly but its just wont give me aything back.

i think i am doing something wrong here but i cannot spot the error in my setup.
i have tested 3 IC's so far and none of them responded anything back. i doubt that 3 out of 3 chips are dead.

here is my setup:
an ftdi uart converter is connected to a logic analyzer and the MCP39F511 (the logic analyzer is mostly a sanity check)
(https://abload.de/thumb/2020-11-2801_15_54-pr9qjtz.png) (https://abload.de/image.php?img=2020-11-2801_15_54-pr9qjtz.png)
 (https://abload.de/thumb/photo_2020-11-28_01-101ksi.jpg) (https://abload.de/image.php?img=photo_2020-11-28_01-101ksi.jpg)

when sending some commands with hterm, the logic analyzer confirms the correct transmission. but neiter an ack or nack is sent back from the MCP:
(https://abload.de/thumb/2020-11-2800_01_08-wigbjmh.png) (https://abload.de/image.php?img=2020-11-2800_01_08-wigbjmh.png)
(https://abload.de/thumb/2020-11-2800_01_26-wi9sk7p.png) (https://abload.de/image.php?img=2020-11-2800_01_26-wi9sk7p.png)

so what am i missing?
thanks in advance!

Title: Re: Can't communicate with MCP39F511 power monitor via UART
Post by: HalfSpace on November 28, 2020, 03:45:02 am

Hi Brathahn,

The MCP39F511 should respond with a CSFAIL 0x51 even if the checksum is incorrect, but getting no response could be an incorrect baud rate setting. If the MCP39F511's were removed from something else or pre-programmed by a supplier, they may have been set to another baud rate than 115.2kbps. Try to send the commands at a lower baud rate and see if you get a response.

Also do a search on this forum for the MCP39F521 which is a I2C version of the MCP39F511. The discussion regarding the MCP39F521 is similar to the problems you are having. 

HalfSpace

Title: Re: Can't communicate with MCP39F511 power monitor via UART
Post by: Brathahn on November 28, 2020, 07:33:35 am

Thank you for the quick reply!

well, this fixed my problem:
https://www.eevblog.com/forum/microcontrollers/mcp39f521-i2c-power-monitor/msg1101038/#msg1101038 (https://www.eevblog.com/forum/microcontrollers/mcp39f521-i2c-power-monitor/msg1101038/#msg1101038)

the datasheet declares an optional 4MHz oscillator on pins OSCI and OSCO. if it detects none, it will switch to the internal oscillator.
so i hooked up my function generator to it, and i could immediately communicate with it.
also tying the OSCI pin to GND worked properly too.
i think the chip measures the capacitance on the OSCI pin to check if there is an oscillator or not.. and the long trace of the breakout board and the breadboard may be the problem.

edit: all three chips are working fine now.