rs232
I need RS232 IC with Features: power supply 3.3v, ESD protection, 8-drivers/8-receivers. I'm looking for ic with these specifications are not found.
These needs can be met if I use two IC is SP3244E (3-driver/5-receiver) and SP3249E (5-driver/3-receiver). My question: Can I use two IC above if I need 8-driver/8-receiver? Thanks.
You need to ensure compatiblity with CTS/RTS 3.3V CMOS and ensure polarity is correct for CTS/RTS TTL.
TTL threshold is 1.2V HCMOS threhold is is Vcc/2 or 1.6V so close enough and should be able to drive 1 TTL load. CMOS input protection over Vcc is all that is needed from 5V TTL. (series 1K and Shottky diode clamp to 3.3V)
It looks like the opto-cable is resuing DTR and RTS as it's own power input pins.
Your MAX3222 uses charge pumps to generate the high positive and negative voltages for signalling over RS-232.
To me, if your cable doesn't draw a lot of current, the easiest thing to do would be to connect the positive supply (DSR) to V+ (pin 3) and the negative supply (RTS) to pin 7 of the MAX3222. Voila, power.
If your cable needs more juice, you'll need to provide it by some other means (a separate power supply or charge pump).
Best Answer
Sure, if the specs of both meet your needs.
Before the MAX232-style charge pump devices came on the scene, it was normal to use a 1488 in the transmit path and a 1489 in the receive path. Perhaps there were bidirectional external-supply-required parts available, but they don't seem to have been very popular; rather most shipping products stayed with the 1488 & 1489 until they went to the charge pump solutions.