What is an RS-232 level converter circuit?
The AVR has a serial interface built-in (pins 2 and 3) and the Clock firmware has extensive support for this serial port. The voltage levels generated on these pins are 0 (Low) and +5V (High) and are available on the middle pin of the PCB headers marked TXROUTE and RXROUTE. However, these are not the voltage levels used in the RS-232 Serial Interface specification, as used by a PC for example. Those levels are approximately +12V (Low) and -12V (High). A special IC (MAX232A or equivalent like the HIN232A or SP232A) is usually used to do this voltage level conversion. This IC (IC5 on the PCB) requires four external capacitors (0.1uF) to do the work; it uses another 0.1uF capacitor for its own power stabilization (these are C12-C16 on the PCB). There is also room for a standard serial DB9 connector on the PCB (X1) as well as a 3 pin RS232 header (as available on the original AVR Oscilloscope clock.) If the user wants the AVR Oscilloscope clock to communicate with a PC, some RS-232 level c
