OT: USB to RS232 converter?

On Fri, 12 Oct 2012 10:15:00 +0100, "N_Cook" put finger to keyboard and composed:

PuTTY is another popular freeware terminal emulator:

- Franc Zabkar

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links/

-

it,

I've unzipped the hyperterminal1 one on that page and obtained a USB to RS232 converter "dongle". The Win7 complient driver opens ok under win7 and established a serial port as COM3 (in Device Manager) on plugging in. Opening hyper, set up a 9600 serial. The intended use is 25w D serial . So far I was a bit rushed and think I had 2 hypers up and operating into COM3 , but no LED flicker connecting pins 2 and 3 together on a RS232 checker with

25 to 9 adapter. Hopefully more time available in the next week.

On Sun, 14 Oct 2012 08:34:50 +0100, "N_Cook" put finger to keyboard and composed:

I'm not sure what you are trying to say, but when the Tx and Rx pins are looped back, you should see an echo for each key that you type. If there is an echo when the Tx and Rx pins are open, then you would need to turn off local echo.

- Franc Zabkar

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YYoouu ddoonn''tt hhaavvee ttoo ttuurrnn iitt ooffff

... but it helps. If you've got characters appearing with no loopback, you'll get *two* of everything with a successful loopback.

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My error, only found when I closed down the win7 m/c, and 2 hyper apps to force closure to. Just tried again and now LED flicker commensurate with baud setting and ASCII text echoed to screen for text file "sent" with pins 2,3 xconnected. So when I can clear the decks and get back to the real use, it should work, thanks for the assistance in unravelling this topic.

Since CP/M days and dumb terminals I've always checked an RS-232 link with simple LED checker that I made a mod to, of a switch between p2-p3, to check that if ascii is sent then ascii is echoed back to the VDU (termed in those days ISTR) and not garbage on the screen and the LEDs flicker at a rate varying from slow 110 baud to whatever fast upper setting. Another reminisce , I first went onto this internet malarcky with a 300 baud modem

This is UK "Maplin" badged 10 quid USB-RS232 converter with Prolific chipset with win7 on the box and a CDrom. As always? with these adaptors the spec on the box or manual only refers to speeds up to ... , never down to .... , T got no help from store "assistant". There was an engineer in the shop when I was there, saying he uses exactly those ones for updating/transfering from laptop USB to RS232 industrial process controllers, sometimes at 2400 baud and usually 9600 baud. As the assistant said, "I've learnt something today "

Not tried in ernest but setting this , unzipped on win7 starter

to paper tape speed 110 baud the LEDs flicker pedestrianly on the serial line checker so presumably can go from 110 baud , through the required 9600 to the 500K or whatever

According to the PL-2303 data sheet (which you can find on line), the device can be set for any combination of start bits, stop bits, and parity you might want, and uses a programmable baud rate generator which covers the range from 75 baud to 1,228,800 baud. Those parameters should be settable using whatever sort of terminal emulator app you have.

The current capability of the chip's output pins is nowhere near that of a "real" RS-232 device, and the voltage is likely to be a lot lower, so it may not be able to make the LEDs in a tester light up. Also, the signal levels may be inverted from "standard" RS-232.

Isaac

It's a TTL device.

RS232 is a VOLTAGE interface, with the original spec being -15/+15, then it was reduced to -12/+12, and some improperly designed interfaces send -5/+5. The voltage must cross 0 volts.

TTL devices are CURRENT interfaces. They use +5 (or 3.3) volts to stop a current flow, and ground to allow one. Some RS-232 interfaces mistakenly accept the ground as the same as -12 volts and the +5 as +12.

It is inverted because the RS-232 spec is that -12 is 1, and +12 is 0.

If you want to make a proper RS232 interface from a USB bridge chip, you need a voltage converter chip the MAX-232 are the most common because they have built in DC to DC converters to provide the higher voltages of both polarity.

You have to be careful because some devices have actual RS-232 interfaces, while others have TTL. Most Japanese, Chinese and Motorola radios have TTL interfaces, while Tait radios use RS-232.

I don't know about any other devices, except modems, but I'm not sure anyone has one these days.

Geoff.

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it

send -5/+5.

I measured, no load, -10V on one of the pins of this Maplin/prolific one. The converter works where intended and the piece of kit can now be taken out on the road and function changes made via a win7 10 inch notebook pc rather than win98 desktop machine

isw wrote in news:isw-515EC4.21184014102012@[216.168.3.50]:

I have the Maplin ZP43W Prolific PL2303 chipset USB serial adaptor, which as I *think* it is the only one of its type in their range so is almost certainly the same as N_Cook's one.

It certainly has enough drive capability to light high efficiency bicolour LEDs while maintaining adequate signal levels for a MAX232CPE chip. My RS232 TTL serial level converter board's LEDs have 8.2K series resistors and I am seeing approximately +/- 6.2V levels when loaded by the LEDs and the MAX232. Off-load I see +/- 6.4V levels.

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I forgot it did have the load of the checker LEDs

Removed a sticker and can just read through the blue translucent plastic, 28 pinner is PL2303 then suffix HK or HX perhaps, the other 28 pinner or so not readable E no. is clear E315599