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I am trying to make a PCB for TTL to RS232 converter. I am using the MAX3232.
It looks 10-11, 14-7, 13-8 and 12-9 are the same. I see some diagrams where people only use one of them. For example,in this diagram:
What should I do? Connect both or just one?
I am trying to make something like this:
Many RS232 peripherals use control signals, e.g. CTS/RTS, in addition to the TX/RX data lines, so they would need another transmitter/receiver.
If you plan to make a general purpose RS232-DB9 module, you can use them as CTS/RTS signals or any other signal that would suit your need.
Here's a picture of the various RS232-DB9 connector pins (source):
It has two inputs and two outputs. What you do with them or not depends on what your application requires.
You can make an RS232 adapter with two RS232 ports that both only support TXD/RXD, or you can make one port that supports RTS/CTS handshaking too, or you can choose to leave parts of it unused like on any other logic gate.
And like with any other logic gate, you must read the datasheet if an input can be left unconnected due to internal biasing, or does it require to be connected to some potential like VCC or GND.
Although if such a board already exists, consider if it is worth making it yourself or buying.
I would only say that there is also 2 others outputs ... generally not known and not used !
Theoretically, ~ +5V and ~ -5V ... (~ +9V and ~ -9V if "some" supplied with +5 V) which can be used for bipolar supplying op amps having low quiescent currents ... (pin 6 and pin 2 in the OP picture, it should be interesting use of 1 uF capacitors C1-C2-C3-C4 in this case). From MAX232 note, link page 4.
https://www.renesas.com/eu/en/document/dst/icl232-datasheet , see figure 11.
Additional remark : I have found a remark (? for old products) about C3. It was better (?) to connect Capacitor C3 to VCC (5V) such that it is compatible to both Texas Instruments and Maxim Integrated chips ( MAX220-MAX249, C3 pin 2 connected to Vcc). And Renesas too ... All are now "aligned" for connecting pin 2 at Vcc or ground (TRSF3232 , TRS202).
