I'm making software UART (TTL levels) on ATtiny85. Need I connect current-limiting resistor to output (TX) port? If "yes", what value should I use?
I plan to connect my device to a UART-USB converter (on PL2303, FT232, etc.).
TTL RS-232 current limiting
avrrs232uart
Related Topic
- Electronic – How to know whether a random “known not TTL” RS232 device will work with any old random USB-RS232 converter
- Electronic – How to setup a RS-232 Cape for BeagleBone Black
- Electronic – Sparkfun RS232 Shifter SMD TTL Waveform DC Offset
- Electronic – Reading UART from device that has floating ground
- Electronic – What kind of serial cable do I need? (TTL vs RS232)
Best Answer
No, you can connect the ATmega directly to the FT232 etc.
In general, a TTL or CMOS level output does not need a current limiting resistor when connected to an equivalent input. Reasons to include a current limiting resistor can be
damage limitation when the output is accidentally connected to ground, power, or another output
damping of oscillations & limiting edge speed, both mainly for relatively long connections (not likely to be needed for the design of average PCBs)