Serial / USB to serial port troubleshooting

Last modified by Eric Nantel on 2023/01/24 10:28

If you are experiencing trouble communicating using the serial port or a usb to serial cable these are almost always issues with the PC. Here is a list of some of the most common problems. These suggestions pertain to the SSC-32 communications AND the Bot Board II programming.

I can’t connect to the SSC-32 with any of its PC applications, LynxTerm, RIOS, SEQ, or PowerPod.
The green LED on the SSC-32 is a status indicator, not a power light. If this LED does not illuminate then you have a power problem. When power is first applied the LED will light up steady telling you it’s 99% functional. The LED will go out after it has received its first byte of data, and then blink after that when it’s receiving data. This will happen even if the baud rate is wrong. It’s a useful tool for troubleshooting the communication system.

Note: LynxTerm, RIOS, SEQ and PowerPod all send commands to the serial port continuously when first opened. It’s possible that the LED is on for such a short time it appears to never go on. Remove the serial connector and try again.

If the green LED never lights up.
Make sure your VL terminal has from 6vdc to 9vdc connected to it. Red is positive and black is ground. For now remove the VS1 = VL jumper to isolate the servo power from the logic power. If possible check it with a VOM meter.

Note: LynxTerm, RIOS, SEQ and PowerPod all send commands to the serial port continuously when first opened. It’s possible that the LED is on for such a short time it appears to never go on. Remove the serial connector and try again.

If the green LED never goes out.
This is a sure indication that your program is not talking on the right serial, or “com” port, or the com port is defective, or the serial cable or USB to serial cable is defective, or the serial port enable jumpers are not installed on the SSC-32.

Normal DB9 serial ports, indicated by the 9 pins sticking out of the D shaped metal part are normally numbered as com1 or com2. Try changing the com port to a different number. If you don’t have a serial port it’s easy to add one.
We will discuss USB to serial cables separately.

What USB to serial cable should I use?
We recommend only high quality name brand adapters. With these devices you literally get what you pay for, so don’t skimp. Look for cables that use the FTDI driver chip if possible. We highly recommend the FTDI UC-232R-NE ChiPi cable 115. Others have reported good results with the following cables. Belkin F5U409, BAFO BF-810, I/O Gear GUC-232A, Keyspan USA-19HS, Dynex DX-UBDB9, etc. Although these adapters have worked in the past, with manufacturer changes, and new operating systems emerging, there is no guarantee they will continue to do so. The only USB to serial adapter we know will work for sure the the FTDI.

**When using the FTDI cable we recommend the following changes within the driver settings. **
With the USB to serial cable plugged in and recognized by Windows go into:

control panel
device manager
Ports (COM & LPT)
USB Serial Port (COM?)
Port Settings

Make sure the receive and transmit transfer sizes are 4096, and change the latency to 1. Click ok then ok. Then close the rest. The latency is the delay before sending data. If it’s too long problems arise.

If you plan to do a lot with this hobby and want a trouble free interface then install a real serial port as illustrated here. USB to serial cables do work, but some can be finicky to optimize for the best operation.

What USB to serial cable should I avoid?
Nikkai USB to serial converter
Pololu USB to serial converter No. 391
Anything from e-bay for less than $15.00

My USB to serial cable doesn’t work properly, or is slow.
Check the power mapping for the USB ports. The mapping defines how much power each port has available to it. Some USB devices will take up to 500mA of power. Some mapping actually shares this 500mA with 4 or more ports. Insufficient power can cause problems. Some users mention they had to use a powered hub to get the adapter to work, especially with laptops.

Some PC’s use a serial channel for IR communications. Apparently it’s possible for this same channel to be selected by a USB to serial cable. A user reports changing the default com port from 6 to 7 fixed a speed issue.

The serial port settings may need to be changed to ensure the optimum performance. Look at the FIFO transmit and receive buffers. Some machines will have the two values off by one. They need to be the same and larger than one. So 4 and 4 or 8 and 8 or 14 and 14 all seam to work.

For FTDI based adapters. They have settings called Latency and buffer that can help with the speed. Under the advanced setting of the com port in device manager should have this. Reducing the buffer size to 1k and Latency from 16 to 3 or even 1 should improve the speed significantly.

For Prolific based adapters. Ensure you have the latest driver if you are experiencing problems.

Sometimes I can program the Basic Atom and sometimes I can’t.
Sometimes the applications recognize the SSC-32 sometimes they do not.

One thing that is not apparent is that the serial port is only available to one program at a time. Usually the first program that uses the serial port will not allow other programs to use it. After the program is closed the serial port will be available again. You can also add an additional serial port if you want to, for example, be able to program the Atom and connect with the SSC-32 at the same time.

Created by Eric Nantel on 2023/01/24 10:26
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