NNoott LLooccaall EEcchhoo

Okay, from what I've gleaned, it seems as though the serial connector on the car docking sled is already "crossed over", i.e., TD to RD and vice-versa. Meaning that you can't use the supplied null-modem cable to connect to the car docking sled, you have to use a straight-through cable for that job. (If anyone can confirm this for sure, I'll add it to the FAQ.)

I'm trying to make an adapter plug that will allow me to connect the supplied null-modem cable to the serial port on the car docking sled. It works, but I have a problem.

When I am in Hyperterminal, each character I type is ddoouubblleedd lliikkee tthhiiss.. Everything else seems to work at the player's shell prompt except for this echo.

I know what you're thinking: Turn off local echo in Hyperterminal. But it's already turned off!

What have I wired wrong to cause this?

Here is what I have wired:

Pin1 = Pin1 (Carrier Detect)
Pin8 = Pin8 (Clear To Send)
Pin2 = Pin3 (Crossed Recieve/Transmit)
Pin3 = Pin2 (Crossed Transmit/Receive)

That's all.

When I make it 2=2 and 3=3 it doesn't work at all, so I know it's not that.

Any ideas?

sounds like a short between tx/rx.

But of course, you wouldn't be able to enter most commands if that were the case.

As far as I can tell, there is no short between TX and RX, and all commands work perfectly. It is literally behaving as if I've got local echo turned on, but I haven't.

Now it seems to be magically working right. Difference is that I have also connected the audio outputs and ethernet to the player.

I take that back, it's intermittent. Sometimes it works, sometimes it doesn't.

Sometimes it works up until I try to "Q" the player to the shell prompt, then I get garbage and I can't see anything from the player (but my typed commands still work and I can type "exit" and get the player to restart).

Must be an intermittent wiring connection somewhere, I guess I should actually solder the connections instead of crimping them.

Maybe you need to hookup the ground (pin 5 IIRC)?

Phil

I forgot to say that I tried that, too. (5=5) Didn't change anything.

I just did a logo upload that worked, and I'm in the middle of installing a fresh Hijack kernel via serial and it looks like it's working, so I'm not gonna worry about it too much.

Yeah, Hijack install just finished OK, should be fine I suppose.

I'm trying to make an adapter plug

Go to RatShack and spend $2 on a null modem adaptor (which will uncross your crossed cable). Just like ethernet cables, it isn't worth the trouble of making your own.

-Mike

Using the car/sled connector I haven't had any problems using a straight through cable to a PC i.e. every pin 1->1, 2->2.

I did already confirm that the sled connecter was a DCE interface and not a DTE interface like the one on the empeg itself. Perhaps you never saw that thread (don't know how you didn't though )

As for the echo, if it's uploading a kernel OK, then that really should cause problems. The fact you say intermittent reallys tends to suggest an intermittent short between TX and RX.

When it's echoing, try unplugging from the empeg so you only have the cable connected and see if you get one copy of every character typed.

I am not sure, but I think that RTS and CTS need to be crossed in a null modem cable. (7-8 and 8-7). If you are using no flow control though, it may not matter. Does the empeg use hardware contol if the signals are there? or does it always just use 3-wire setup?

From what I understand, flow control has to be totally off when you're talking to the empeg.

However, pin 8 is connected on my circuit because it's wired in the serial connector. Should it not be connected if there's no pin 7?

If no flow control or handshaking is being done, then I would only connect the 3 wires. 2-3, 3-2, and 5-5. I am not sure why pin 8 would need to be available on the empeg if no handshaking was used.
Ah, just looked on the developer info page. It says pin 8 is being used as the headlight sense. In that case, I would not hook up pin 8. If you hook up pin 8, it then is swapped in the empeg supplied null modem cable to the RTS signal, which is an output from a DTE.
If the RS232 connector on the sled is swapped, and therefore a DCE, then it is strange that the headlight sense would be tied to pin 8, which is an output on a DCE.
Perhaps it means that headlight sense is tied to pin 8 on the RS232 connector in the empeg itself. That would make more sense, as that is a DTE, and pin 8 is then an input.

Greetings!

Don't know if you're still seeing this, but (if you have an older unit, and I am guessing you do) there was a problem with the serial connector on the sled where power and ground were not connected properly... Might this help?

If no flow control or handshaking is being done, then I would only connect the 3 wires. 2-3, 3-2, and 5-5.

This seems to work OK... But I don't understand why. Seems odd to me that you wouldn't even need the CD pin? Why are pins 1 and 8 not needed?

I was going by the pins that were already used on the docking connector according to the description at the developer info section of riocar.org.

CD, Carrier Detect, is a signal that is part of the RS232 spec so that modems could tell the DTE that there was a good carrier. It is an output from a DCE. Its main use is in modem applications. Since both a pc and the empeg are DTE devices, they dont need that pin. With handshaking, it is kinda all or none. Using CTS would require using RTS aswell.
I dont have a sled with me, so I cant test the connections, but it seems that pin 1 and 8 are connected the way they are for some purpose other than serial communication.

Okay, thanks. Looks like it's 3 wires in the docking sled for me.