I recently posted a query about an RS-232 to LVTTL converter circuit. Thanks to all who replied. I built the circuit and it seems to work fine. The rising edge is a bit leisurely. The falling edge is pretty fast.
For reference, here is the actual circuit I ended up building. (Use courier or other constant-width font for ASCII art schematic):
VCC (5V) | / \\ R2 (1k) / | +----------------+-> to LVTTL device | | R1 (10k) /c / RS-232->---/\\/\\/\\/\\--+----| Q1(mmbt2222a) \\ R3 (1k) | \\e / /e | | D1(mmbt2222a) +--| | / | \\c | \\ R4 (1k) | | | / +---+--+--+ | | | GND GND
As you can see, D1 is a diode-connected transistor. I did this because we have lots of mmbt2222a's, and no SMT diodes in stock.
--Mac