i'm currently using this reference schematic to wire up 10 RS232 slaves in a "multidrop" configuration (The slaves are some ATMEGA328P with MAX232 Trancievers in order to make a real RS232 network).
I have some doubts regarding the diode to put on TX line of slaves: i've tried using LL4148 (Datasheet here) but nothing works, the slaves will not work as expected.
So, i've taken a BZX85C5V1 Zener diode and i've replaced the LL4148, now the slave works as expected: receiving and sending messages to the master.
What i'm missing? maybe i've chosen a wrong diode (LL4148)? which diode i can use in this multidrop serial network configuration? Why 5V a zener (BZX85C5V1) works?