[RESOLVED] RS232/485 to TTL Connection

[honeybee]

I have a device that has about six wires sprouting from its back. The device manual says that it can be connected to an RS485 serial port. I am trying to figure out how to map these six wires with the nine pins on a serial port.

On hunting around I learnt I would need some adapter to go in between the two components, the adapter goes by the name Max232.

What I need is some kind of a circuit diagram or electrical wiring diagram that will tell me how to connect which wire from the device to which of the RS232/485 connector pins.

FYI the device wires contain one wire labelled TX/RX- and another wire labelled TX/RX+.

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[Nightwalker83]

What is the device for?

[Shaggy Hiker]

I believe that what the Max232 does is change the voltage levels so that you don't fry your TTL device which, on it's own, is running at 5V or less rather than the higher voltage found on RS232. Aside from that, I haven't actually wired in a Max232, so I can't say more about it.

[dilettante]

Almost cheaper to just buy one assembled or as a kit:

http://www.compsys1.com/workbench/On...3_adapter.html

That link was for TTL/RS-232, but you should find plenty of RS-485 converters online too.

[IanS]

The MAX232 chips is TTL to RS232. I've used it many times.

The reason that the MAX232 chip is interesting is that it can produce RS232 signal levels +/- 12 volts without actually have a 12v supply. It just requires +5v and uses capacitors to generate 12v internally.

I have no idea why somebody would tell you to use the MAX232 to connect to RS485.

Unless ... If you already have RS485-to-TTL then of course you can use the MAX chip to do the TTL-to-RS232

But seriously, just go to the RS Online and buy a small RS485 converter. That has the RS232 9pin female connector on one end with 4 screw terminals on the other end for TX+ TX- RX+ and RX-

You said the device has 6 wires. Are they labelled ? TX+, TX- etc ?

[honeybee]

Yep, the wires are labelled:

1. FG
2. TX/RX-
3. TX/RX+
4. VP (DC24V)
5. VG
6. FG

While the pins 1, 5 and 6 are probably used for grounding or loopback, 2 and 3 must be the data connections while 4 is the so-called 'reference' pin. The voltage for this pin is given as DC24V. So another question is, can the device support voltages this high?

The device is a finger-vein reader (the sort where you have to insert your finger inside and it scans for the vein pattern of your finger). The manual is in Japanese, and it does not specify how the wires could be connected to either an RS485 connector or an RS232 connector.

I am taking up this discussion at the older thread I had posted:

http://www.vbforums.com/showthread.p...45#post3941845

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[dilettante]

FG may be "foil ground" (shielded twisted-pair cable). VP may be a supply voltage to power the device (?) and perhaps VG is the power and signal reference ground (?). Are you sure one of those FGs isn't SG (signal ground)?

Half-duplex RS-485 is often used as a bus connector, implying the device may require a special protocol for operation.