darudude

To elaborate on Grumpy_Mike's response ...

but doesn't the RS232 work at 12V?

Normally implemented RS-232 uses -12 V to represent a logic '1' and +12 V to represent a logic '0'.

For communications between digital devices, such as in your implementation, a hybrid system is frequently used where RS-232 signals are implemented with digital logic levels. In this case 0 V is used to represent an RS-233 logic '1' and +5 V is used to represent an RS-232 logic '0'.

Each of the three transistors in your circuit is acting as an inverter, so when, for example, your DTR line is +5 V representing a digital logic '1', the PROG_DATA line is 0 V, representing an RS-232 logic '1'.

Would CTS ever go high in this design?"

Yes, when DTR goes low. But this is only +5 V via R4.

floresta