Results 1 to 7 of 7

Thread: No Serial Output

  1. #1
    Join Date
    Dec 2004
    Posts
    831

    No Serial Output

    I've done a number of TiVo upgrades, and being confident (overly confident?) of being able to recover from most problems with the tools at hand here in my house, I've never bothered to use a serial cable during boot. In a couple of days, however, I will be driving to my sister's house - it's a 2 hour drive - and upgrading her Series I DTiVo. I won't have all my tools at hand, and I've never upgraded a DTiVo before, so I wanted to make sure I would be able to see what was happening on boot, especially during the FlashTiVo cycle. I dug up the serial cable, plugged it into my SA Series I TiVo here, and lo and behold there's no output. There's not more than a couple of millivolts between any two of the three pins on the cable. I checked the cable, and continuity is good. Do I just have a bad serial port on my TiVo, or do I need to change something? Having the IR dongle enabled shouldn't have any effect (or else one could not use both an external modem and a cable receiver), but does it?
    Having trouble with TyTool? Try TyTool Documentation
    Need to hack an S3 / THD? Try S3 Hacking Script

  2. #2
    Join Date
    Apr 2003
    Posts
    2,402
    Quote Originally Posted by lrhorer
    I've done a number of TiVo upgrades, and being confident (overly confident?) of being able to recover from most problems with the tools at hand here in my house, I've never bothered to use a serial cable during boot. In a couple of days, however, I will be driving to my sister's house - it's a 2 hour drive - and upgrading her Series I DTiVo. I won't have all my tools at hand, and I've never upgraded a DTiVo before, so I wanted to make sure I would be able to see what was happening on boot, especially during the FlashTiVo cycle. I dug up the serial cable, plugged it into my SA Series I TiVo here, and lo and behold there's no output. There's not more than a couple of millivolts between any two of the three pins on the cable. I checked the cable, and continuity is good. Do I just have a bad serial port on my TiVo, or do I need to change something? Having the IR dongle enabled shouldn't have any effect (or else one could not use both an external modem and a cable receiver), but does it?
    Are you using a gender changer? A null-modem adapter? Both? Check the continuity between pins 2 and 3 while shorting tip to ring on the stereo connector. It should loop with no resistance. If it does, then the cable is probably good and you need to re-think your adapters.

    ew

  3. #3
    Join Date
    Dec 2004
    Posts
    831

    Serial Port

    Quote Originally Posted by eastwind
    Are you using a gender changer? A null-modem adapter?
    I'm not using anything. There is no signal at all present on either pin 2 or 3 (of the 9 pin). As I stated, the potential difference between any two pins (tip - ring, tip - sleve, ring - sleve) is less than 10mv. It would be pointless to attempt any communications when there is no signal, and swapping adapters isn't going to help until there is a signal to adapt. (Yes, I double-checked and triple checked using the DVM and two different break-out boxes.)

    Quote Originally Posted by eastwind
    Check the continuity between pins 2 and 3 while shorting tip to ring on the stereo connector.
    I believe I mentioned continuity is good. There is less than 1 ohm of resistance on all three leads. The multimeter is 20 Kohm/volt, so the lead impedance is completely irrelevant. I even checked back through the cable to one of the break out boxes, and a signal is indicated whenever I apply even a small, high impedance signal (the DMM in diode check mode) to the tip or ring.

    Quote Originally Posted by eastwind
    It should loop with no resistance. If it does, then the cable is probably good and you need to re-think your adapters.ew
    As I said above - no adapters. There is no signal coming directly out of the TiVo.
    Having trouble with TyTool? Try TyTool Documentation
    Need to hack an S3 / THD? Try S3 Hacking Script

  4. #4
    Join Date
    Apr 2003
    Posts
    2,402
    Quote Originally Posted by lrhorer
    As I said above - no adapters. There is no signal coming directly out of the TiVo.
    Not sure if there would be any signal coming from the TiVo unless you told it to send something. There's no flow control on the port at all (hardware or software). I'll check mine and see what I get.

    ew

    UPDATE: Negative lead on pin 3 and positive on pin 5 I get ~4.5volts on a 0-10volt DC scale. Note: I have a bash console active and serial port logging--YMMV.
    Last edited by eastwind; 09-20-2005 at 04:08 AM. Reason: Update

  5. #5
    Join Date
    Dec 2004
    Posts
    831

    Serial Port

    Quote Originally Posted by eastwind
    Not sure if there would be any signal coming from the TiVo unless you told it to send something. There's no flow control on the port at all (hardware or software).
    The specs for EIA RS-232 require the TxD line be held high (nominally +12V) whenever the port is idle. This represents a logical 0, or a mark. When the line transitions low (-12V), a logical 1 or space is asserted. An output of -4.5 volts is rather low, but many devices can work with less than 5V. It's supposed to be a minimum of around 8V, however many manufacturers have ignored the spec in that respect. OTOH, it could simply be you have characters streaming out the port, causing the average voltage to be somewhat lower than a long mark. Mine has zero volts with no transitions. That is either dead or off. I suspect dead.

    Quote Originally Posted by eastwind
    UPDATE: Negative lead on pin 3 and positive on pin 5 I get ~4.5volts on a 0-10volt DC scale. Note: I have a bash console active and serial port logging--YMMV.
    I thought serial port logging was enabled by default. Not? If not, then it is possible the port is shut down. I was of the impression serial port logging was accomplished simply by redirecting stdout to /dev/tty*. If so, then the port must already be active.
    Having trouble with TyTool? Try TyTool Documentation
    Need to hack an S3 / THD? Try S3 Hacking Script

  6. #6
    Join Date
    Apr 2003
    Posts
    2,402
    Quote Originally Posted by lrhorer
    I thought serial port logging was enabled by default. Not? If not, then it is possible the port is shut down. I was of the impression serial port logging was accomplished simply by redirecting stdout to /dev/tty*. If so, then the port must already be active.
    News to me. I've always set mine with bootpage -P "root=/dev/hda? dsscon=true console=2,115200 upgra...." /dev/hda/

    ew

  7. #7
    Join Date
    Dec 2004
    Posts
    831

    Still no luck

    Yeah, I read up a bit more with your guidance (thanks, BTW), and if I have it right, the serial port is /dev/ttyS3, because /dev/ttyDSS is a link to ttyS3. This being the case, the value for console is set at 3,115200. I did this and no joy. The port is still dead as a doornail.
    Having trouble with TyTool? Try TyTool Documentation
    Need to hack an S3 / THD? Try S3 Hacking Script

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •