max3232 and ftdi cable?

rwgast_logicdesign · 2012-10-28 12:33

so im building a pc based logic analyzer the schematic uses shottkeys and and a 74ls00 used as a buffer for the serial comunications.

i dont have the shotkeys on hand so i figured id use a max3232e. i also have a ftdi usb to serial cable it output 6v instead of rs232s 12. will i have an issue using it with a max3232

Publison · 2012-10-28 12:44

rwgast_logicdesign wrote: »

so im building a pc based logic analyzer the schematic uses shottkeys and and a 74ls00 used as a buffer for the serial comunications.

i dont have the shotkeys on hand so i figured id use a max3232e. i also have a ftdi usb to serial cable it output 6v instead of rs232s 12. will i have an issue using it with a max3232

Could you post the schematics so they can be reviewed?

rwgast_logicdesign · 2012-10-28 13:21

Well im using a max2323e just gonna make a standard data sheet circuit for level shifting so i know the max will be fine for com with the analyzer, I just need to know if theres problems using an ftdi usb to to rs232 cable on the max232's rs232 i/o pins

LoopyByteloose · 2012-10-28 13:50

It is a two part question.
A. Is it safe to use the 6 volt output with the hardware in question. Yes.
B. Will it work. Try it and find out, probably yes.

Mike Green · 2012-10-28 13:59

The MAX3232's RS232 pins are compatible with the RS232 standard signal levels. The datasheet goes into details. The FTDI USB to RS232 cables are compatible with the RS232 standard as well as described in their datasheet. From the block diagram in Figure 6.1, it looks like FTDI uses something like the MAX232 for their TTL to RS232 signal level conversion.

LoopyByteloose · 2012-10-28 14:18

If you have a PropPlug handy, you can avoid all that. I got a BS Homework board with USB to serial adapter and that seems to do TTL direct. I also have a USB programmer for my Pololu robot that outputs serial TTL.

In other words, any one of these will by-pass the RS233 +12/-12 and provide USB to RS233 at TLL signal levels (and I think inverted).

Take a look at all the devices that will progran a Propeller Proto Board that doesn't have the USB chip on it.

I have a new project with an RS232 port requirement that I was thinking I needed a Max3232 chip, but this is so much easer than connecting all those capacitors.

rwgast_logicdesign · 2012-10-28 14:28

well i have a prop plug but im pretty sure it wont work becuase it shifts to 3.3v and i have the serial adapters for arduino that do rs232 to ttl. but i wanted to use the max with a longer serial cable. i ususally have regular rs232 ports at my disposal but i needed to know if the max would be fine when using an ftdi usb to rs232, since its only 6v and not 12. sometimes im on a laptop with usb only. the bs2 serial to ttl works fine with the cable

LoopyByteloose · 2012-10-28 14:42

RS232 has not been providing a full +12/-12 for quite some time and many interfaces don't even bother with the -12 at all.

With the advent of laptops, the +12/-12 became a nasty power supply problem. So voltages were set up to recieve +12/-12 as a safe maximum, but ranges down to +3/0 were quite acceptible. The BasicStamp takes advantage of this and has no -12, just +5/0 which is driven by transistors as they are cheaper than the MAX3232.

I think the MAX3232 is only capable of +9/-9 output at best.

In other words, there is a lot of slop in the RS232 voltage ranges these days. Everyone has found a way to cheat the specification and as long as these work, why bother meeting the standard?

You could copy the BasicStamp interface without the reset circuit - just a few transistors and 10k resistors.

max3232 and ftdi cable?

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