Problem Connecting FT232R USB to ZX Devices

[mikep]

I have several FT232R USB to TTL serial devices. I have noticed the following behavior.

The ZX device has a simple hello world LED flashing program that alternatively turns on the Red and Green LEDs. I tried several different kinds.

I plug in the USB device and the PC assigns a serial COM port. The device drivers were previously installed. No host serial port monitor is running.

The hello world program appears to stutter meaning that the red LED starts to flash several times. After about 2 or 3 seconds, it seems that the ZVM has figured out that there is no connection and the LEDs start alternately flash the red and green LEDs.

This problem does not occur when connected to a regular RS232 serial port.

[dkinzer]

The hello world program appears to stutter meaning that the red LED starts to flash several times.

I suspect that the device driver is toggling the DTR line, causing resets. This hypothesis could be tested by removing the DTR connection to the ZX and repeating the experiment.

[mikep]

I suspect that the device driver is toggling the DTR line, causing resets. This hypothesis could be tested by removing the DTR connection to the ZX and repeating the experiment.

Indeed I just tried that and the "problem" no longer occurs.

This is probably worth documenting in the ZBasic reference manual and the manuals for the various FT232RL based boards (USB-TTL, ZX1280 Dev Board and ZX1281 dev Board). There are two workarounds:

• Disconnect the DTR line unless needed for downloads (already documented)
• Use ATNCHAR - I couldn't find the documentation for this anywhere in the manuals. ZX_NO_DTR doesn't seem to be mentioned either.