Normally Arduino boards are reset by using additional DTR line of serial interface. This becomes a problem when USB-UART adapter doesn’t support DDR line. And you probably read many cases were one or another particular cable won’t work for programming, but can be used for simple serial data transfers. Ralph thought that there should be another solution that would allow using any serial cable for programming. He thought that TXD and RXD lines are always available since they are used for data receive and transmit. So why not to use one of those to reset microcontroller.
With three additional discretes he created a simple circuit that would stand between RXD data line and RST pin. This is simply an RC circuit that would discharge cap during some time. So when data line works in normal operation – RSTin isn’t affected due to slow cap discharge. But when RST signal is held down for longer time – cap is discharged and then RST signal is sent. Since he’s done modifications, he also had to do changes in AVRDude configs. That turned out to be fairly easy. Overall this is quit smart solution that could be considered as option on any Arduino board, so we wouldn’t need to hunt for specific serial adapter cables.