RS232 Cable for Prema 6040 Voltmeter - Page 1
Forum section: electronics / beginners

author: hirada
author_rank: Regular Contributor
timestamp: December 29, 2020, 03:57:51 pm
content: I would like to connect my Prema 6040 to my computer and for that I am in need of a DB-25 to DB-9 Cable. However, next to the serial communcation the 25 pin interface on the device also hosts a current loop, which I am not interested in.The Manual describes the layout of the DB25 connector:1 - Shield/PE(?)2 - TxO3 - RxD4 - RTS5 - CTS6 - DSR7 - GND9 - +12V12 - +20mA13 - +20mA17 - RxC20 - DTR24 - Keyboard 20mA25 - Printer 20mAI suppose, I can omit all the 20mA pins. But I am not sure, about the 12V.The manual further reads (my bad translation): "Since the operation of the 20mA current loop only needs 4 wires, CTS (pin 5) and DSR (pint 6) are to be connected with +12V (pin 9)."So my hope is, for serial communation it is not needed either. Not sure, wether any PC would accept 12V anyway. 12V sounds a little high.My proposal for a cable looks as follows, but maybe someone with more knowledge of serial communations or this voltmeter may correct me. This is just what I believe to have figured out without any real understanding.DB25| DB 91 | -2 | 33 | 24 | 75 | 86 | 67 | 517 | ? (2?)20 | 4The DB25 side of the cable is male, the DB9 side probably female.Any thoughts? I am not sure aboutRxC / pin 17 either.Thanks

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: December 29, 2020, 05:39:15 pm
content: Try a run-of-the mill serial cable:http://hardwarebook.info/Two-Wire_Modem_(9-25)

author: ledtester
author_rank: Super Contributor
timestamp: December 29, 2020, 06:24:35 pm
content: QuoteWikipedia says RS232 voltages can reach +/- 15 volts:https://en.wikipedia.org/wiki/RS-232#Voltage_levelsJust connecting receive, transmit (RX <-> TX, TX <-> RX) and ground should work for you, at least that's what I would try first.

author: hirada
author_rank: Regular Contributor
timestamp: December 30, 2020, 03:16:40 pm
content: Thanks. I've tried a standard cable, with RX <-> TX, TX <-> RX, but without success. As only baud rate and stop bits are documented, I believe I've tried all combinations of parity, flow control and databits, but to no avail so far.The cable is layout as follows:DB9 - DB251 - 82 - 33 - 24 - 205 - 76 - 67 - 48 - 59 - 22I may try jumpering all pins but rx/tx next.

author: m k
author_rank: Super Contributor
timestamp: December 30, 2020, 05:31:40 pm
content: 2-23-34-65-76-207-58-4

author: hirada
author_rank: Regular Contributor
timestamp: December 30, 2020, 06:40:27 pm
content: That m k. That's it. Adding a Nullmodem adapter to above cable makes stuff work. Somehow I've been under the impression, the 2-3/3-2 would be the crossing part.Just as a reference for future generations with interest in state of the art high tech:Code:# picocom -b 19200 -p 1 -y n -d 8 -f h /dev/ttyUSB0picocom v3.1port is : /dev/ttyUSB0flowcontrol : RTS/CTSbaudrate is : 19200parity is : nonedatabits are : 8stopbits are : 1escape is : C-alocal echo is : nonoinit is : nonoreset is : nohangup is : nonolock is : nosend_cmd is : sz -vvreceive_cmd is : rz -vv -Eimap is :omap is :emap is : crcrlf,delbs,logfile is : noneinitstring : noneexit_after is : not setexit is : noType [C-a] [C-h] to see available commandsTerminal ready+**10.873691*M P08B3B1DV0F0T8+**10.873686*M P08B3B1DV0F0T8Not sure, why the batterys measured here are losing a good volt per minute, but that's another story for sure.