Problems with RS232 serial port communications

Contents

  1. Problems with RS232 serial port communications
    1. Problems communicating with GUI
      1. GUI does not find a Lithiumate BMS
      2. Wrong baud rate
    2. Problems communicating with a terminal app (PuTTY)
      1. Unable to open COM port
      2. Blank screen
      3. No communications, yet 5 V LED is on
      4. Shows home menu, won't take input
      5. "D'de loves Ann"
      6. Continuous line feeds
      7. Garbled data
      8. Garbled data in the presence of noise
      9. Hex data
      10. Reverts to previous menu
      11. USB hangs-up
    3. Problems programming
      1. Changes don't take effect
        1. With GUI
        2. Command line (PuTTY)
    4. Garbled screen in the Test menu only

Problems communicating with GUI

GUI does not find a Lithiumate BMS

These are some possible reasons that the GUI does not find a Lithiumate BMS:

Wrong baud rate

To communicate with the GUI application, the RS232 rate of the BMS controller must be 57600.

If you change the RS232 rate, the GUI application will stop talking to the BMS controller, but will still talk to a terminal application.

To fix it:

Problems communicating with a terminal app (PuTTY)

Unable to open COM port

The terminal application doesn't open the COM port (Unable to communicate with USB/RS232 adapter, if applicable)

Blank screen

The terminal application shows nothing

No communications, yet 5 V LED is on

Most likely, you have a bad crimp on pin 1, and the connection intermittent. If you pull on the wire on pin 1, I bet you it will pull out.

If pin 1 is not making contact, the ground current is going through pin 9 instead, which places some resistance in series with it. Because of that resistance, inside the BMS master the 12 V supply drops down to something like 3 V; that's enough to light an LED, but not enough to power the BMS.

Shows home menu, won't take input

The terminal application displays the normal home menu (refreshed every 16 seconds), but then doesn't respond to any key press.

Either there's a loose connection on the RS232 RX line, or your terminal is hung up. No need to restart the BMS controller: it is running fine.

"D'de loves Ann"

The terminal application shows "D'de loves Ann", and nothing else.

Continuous line feeds

The terminal application shows a cursor starting from the top left and moving down to the bottom left, and nothing else.

Garbled data

The terminal application (PuTTY) shows garbage

The terminal application may be set for the wrong baud rate.

The BMS master may have forgotten the baud rate for the RS-232 or USB port:

Garbled data in the presence of noise

The terminal application works normally until a source of EMI (charger, motor driver) comes on; then, it shows garbage.

The RS232 link is not balanced (unlike the CAN bus) so it has poor noise immunity. Therefore, it is not intended for continuous use in the system, but just for initial set-up and troubleshooting.

Having said that, if you do try to use the RS232 as a permanent communication link in your application, then:

The workaround we used most effectively was to put 1 kOhm resistors in series with the 3 lines in the RS232 connector: GND, RX and TX. You'll need to make yourself a little adapter with a male DE9 and and a female DE9, and connect pins 2, 3 and 5 of the two connectors using 1 kOhm resistors.

Hex data

The terminal application shows a string of hex data

Reverts to previous menu

When making a menu selection (by pressing a digit) the terminal application reverts to the previous menu.

USB hangs-up

There is a bug in the Windows drivers that cause the USB port to hang up in the presence of electrical noise. The only way to restore communications is to unplug the USB connector from the computer, and reconnect it. This is a Windows issue, and there is little that we can do on our end.

One trick we have used is to put 3 resistors (1 kOhm each) in series with the 3 RS 232 lines: Gnd, RX and TX. It keeps the USB port from hanging up.

Problems programming

Changes don't take effect

When changing a parameter, it stays the same.

With GUI

Command line (PuTTY)

Garbled screen in the Test menu only

There was a batch of badly programmed BMS controllers, between S/N F650 and F700. We have reprogrammed most of them, but there are still a few stragglers: 655-658; 660-665; 668; 670; 681; 684; 691

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