Can you provide some more details to your question? Digi sells part 20-101-1183, a USB programming cable that includes an FT232RL IC. I see the BAT54 diodes in the schematic:
My guess is that the RCM32xx includes pullup resistors on the RXA and /RESET pins, and the diodes ensure that the FT232RL will only pull those pins to ground and won’t drive them with a voltage possibly higher than the board’s Vcc.
If you’re trying to build an alternate programming cable using an FTDI TTL-level USB serial cable, then you’ll need to understand the Digi programming cable schematic and the wiring between the programming port and the rest of the RCM32xx. If you’re trying to build a cable to power the RCM32xx and program it when not installed, then the BAT54 diodes might not be necessary.
i am using a serial usb converter with the ftdi chipset (but not the cable from digi). but I have modified (adding components) according to the schematic of the digi. when it is used an error occurs when sending the pilot bios.
This is the rcm32xx module that I will program. (this module is working fine, I just want to try writing a program on this module)
I can’t view that document. What’s the error? Can you monitor the serial communications? Make sure you’re using a short ribbon cable to the RCM3200, and double-check your connections. I’d recommend just getting one of the Digi cables and using that, or as a baseline to compare to your hardware. Once you have code on the module, you can read/write to serial port A and test whether your cable can pass that data back to the host.