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don't worry, one day you will grow old and
1. have "trouble remembering dates"
2. have plenty of old stories of when 'she wasn't happy with what you got' so you're taking the safe option
3. not really give a sh*t because it's only retail hype
4. have a backache (women have headaches, men have backaches - because we do proper hard work.)
anyway if the above doesn't fully wash you can make up for it later ... when prices of respective gifts are more sane and/or restaurants aren't jammed up with long waiting queue's...
Maybe someone's serial cable fu is better than mine. I'm looking for some practical insight on serial communications at the PC level. Older machines, larger boxes may still have built in com ports exposed at the back, but most of us are living in the land of usb to serial. For the sake of discussion, the ports in use are confirmed to have the same settings - 9600 baud, 8 bit, 1 stop bit, no handshake or anything else....
Living in the embedded world, we'll solder up a home made serial cable in a few minutes - DB9 to DB9 - connector pins 2-3, pin 5 for the ground (swapping pin 2 and 3 gives you a null modem cable). On the embedded hardware, this is typically all we need to do... but I'm finding PC level usage of this hand crafted cable problematic. If I take a typical null modem cable: 10 ft DB9 RS232 Serial Null Modem Cable | Null Modem Serial Cables | StarTech.com[^] everything works fine.
If I take my stripped down special, no communications. I've verified that both cables are wired the same - with the exception that the commercial product connects the other 6 pins according to standards. I've been told these other connections are not necessary, but said engineers are talking to embedded hardware not another PC.
Wondering if an CP folks have some practical scars and insights in this area that would shed some light on this behavior. I'm going to tell the customer to go buy a serial cable, but now I'm curious.
<italic>Stuck in a dysfunctional matrix from which I must escape...
"Where liberty dwells, there is my country." B. Franklin, 1783
“They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759
People ask me why I still hang on to my breakout boxes, you just never know... I do agree with Munchies_Matt though, it's probably a hardware handshake issue.
"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst
"I don't drink any more... then again, I don't drink any less." - Mike Mullikins uncle
Older machines, larger boxes may still have built in com ports exposed at the back, but most of us are living in the land of usb to serial.
surprisingly even the latest motherboards often have a serial header - pretty standard layout, it's the case manufacturers that don't provide the header. I believe there are headers out that that just replace one of the expansion card slot covers with a DB9/25 and plug via a short ribbon into the mobo header.
Another option I've seen used are boxes that connect serial via network (RJ11/45 one side, 9 pin t'other)
- really handy for connecting remote items (i.e. old manufacturing equipment) where there's already network cables/routers running nearby.
- usually have a web interface for setting the serial options as well as IP address etc (no need to fart about with dip switches)
- have a few different modes of operation... the easiest is it makes the device look like any other TCP/IP connection/stream (as a TCP/IP client)
- all the serial madness set/hidden in the web interface = (in above mentioned mode) no need to use for example the .Net Serial Comms API which [BTW, barely maintained] although not bad does have quirks - particularly if the device/cabling is a bit flaky or keeps dropping/closing the serial link.
I made a bunch of various such cables back in the 90s, and three-wire doesn't always get the job done.
Not everything I had to connect used EIA 232 (RS-232). All of our terminal servers were from DEC so EIA 423 (DECconnect) was most common and there were also some others.
Eventually I wrote up a Word document with all the pinouts I knew and the types of cross-wirings I had to make. I still have the document, but some of the diagrams are missing because I hadn't inserted them properly.
The last time I had to make such a cable was to connect a DB9 RS-232 USB adapter to the MMJ DECconnect console of one of my AlphaServers and it didn't work reliably as three-wire. It doesn't help that the MMJ console port is flaky.
It depends on the pin-out of whatever you're connecting it to -- "standards" is often considered an optional term, in serial comms.
RS232 only uses three wires, but not every manufacturer always uses the same pins.
What I often do is cut the end off an RJ45 (Ethernet-style) cable, and solder it up to the pins of the DB9 or whatever as described in the manual for the serial device (or by using a meter to find which pins are used).
You can afford a bit of trial and error (mixing up Tx and Rx is quite easy, because a wire that's Tx at one end is Rx at the other, and the documentation for serial devices can be confusing, on that point), because it's only comms voltage, so you won't burn anything out.
I wanna be a eunuchs developer! Pass me a bread knife!
3/4's of the way down are diagrams for null modem / crossover cables. See also the diagram after the null model cable, on the software handshaking cable. Even if you don't use software handshaking, wiring it up that way is a good idea.