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Re: [midatlanticretro] RS232 Again?

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  • telmnstr
    ... There are cables that are USB to TTL Serial. They are mostly used with programming microcontrollers. Some are 3.3v, some are 5v, some are switchable. These
    Message 1 of 12 , Jul 11 8:45 AM
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      > My main concern though, were the required voltage levels. It seemed that
      > the Seagate drive wanted TTL levels. So it was recommended that the use
      > of an RS232 to TTL adapter be employed. I didn't have one of those, but
      > I did have a USB-to-RS232 adapter. I figured that unless the adapter
      > employed some sort of voltage doubler to get the voltages up to the
      > normal Rs-232 levels, I would be safe with the 5 volt USB power. Well
      > that didn't work. See my overclock post above for more details.


      There are cables that are USB to TTL Serial. They are mostly used with
      programming microcontrollers. Some are 3.3v, some are 5v, some are
      switchable.

      These are different than the usb to rs232 serial cables.

      http://www.ebay.com/itm/1pcs-New-USB-2-0-to-TTL-UART-Module-5pin-Serial-Converter-CP2102-STC-5pin-cables-/400524483249?pt=LH_DefaultDomain_0&hash=item5d411e9ab1

      http://www.ebay.com/itm/6pin-FTDI-FT232RL-USB-to-Serial-adapter-module-USB-TO-TTL-RS232-Arduino-Cable-/400356015296?pt=LH_DefaultDomain_0&hash=item5d3713fcc0

      I did the same thing you are doing and used one of those FTDI cables, only
      mine I think came from Adafruit.
    • Mr Ian Primus
      ... It DOES contain the necessary charge pumps to create the proper RS232 voltage levels. There now exists a chip, the MAX232, that, when coupled with a few
      Message 2 of 12 , Jul 11 8:50 AM
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        > My main concern though, were the required voltage levels. It
        > seemed that the Seagate drive wanted TTL levels. So it was
        > recommended that the use of an RS232 to TTL adapter be
        > employed. I didn't have one of those, but I did have a
        > USB-to-RS232 adapter. I figured that unless the adapter
        > employed some sort of voltage doubler to get the voltages up
        > to the normal Rs-232 levels, I would be safe with the 5 volt
        > USB power. Well that didn't work.  See my overclock
        > post above for more details.

        It DOES contain the necessary charge pumps to create the proper RS232 voltage levels. There now exists a chip, the MAX232, that, when coupled with a few capacitors, can generate proper RS232 levels with only a 5v input, and serves as a complete receiver/transmitter package, replacing the 1488/1489 pair and it's required voltage sources.

        So, you can use one of those chips to build a very trivial RS232/TTL serial interface, then connect it to your RS232/USB adapter, or to the RS232 port on a computer or terminal.

        -Ian
      • Bill Sudbrink
        ... Those cables are also useful to tie into a cassette interface circuit in a vintage machine and feed serial data straight in without having to mess with
        Message 3 of 12 , Jul 11 8:52 AM
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          telmnstr@... wrote:
          > There are cables that are USB to TTL Serial. They are mostly used with
          > programming microcontrollers. Some are 3.3v, some are 5v, some are
          > switchable.

          Those cables are also useful to tie into a cassette interface circuit
          in a vintage machine and feed serial data straight in without having
          to mess with creating audio files.

          Bill S.
        • Dave McGuire
          ... This cracks me up every time it comes up. Async serial (which includes RS232) is EVERYWHERE. Enterprise networking equipment, large-scale servers,
          Message 4 of 12 , Jul 11 9:34 AM
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            On 07/11/2013 11:32 AM, RonK wrote:
            > I thought you guys could appreciate this.
            >
            > I've been trying to "unbrick" a Seagate SATA 750 GB barracuda hard
            > drive. The recommended approach is to go through it's 4-pin jumper
            > connector to reach its serial port.
            > http://www.overclock.net/t/457286/seagate-bricked-firmware-drive-fix-with-pics/240#post_20364127
            >
            > It's "Back to the Basics" of RS232 technology. Oh no! Would I
            > really have to open that trapdoor in my brain that I hadn't accessed
            > for thirty years, and pull out all the old stuff? I guess so. Baud
            > rate, Parity, STOP bits, Flow Control- oh all that wonderfulness...
            > here again!

            This cracks me up every time it comes up.

            Async serial (which includes RS232) is EVERYWHERE. Enterprise
            networking equipment, large-scale servers, embedded systems, everything.
            It's no longer present on most current PC hardware, but they're very
            much in the minority in terms of how many computer-containing devices
            exist out there.

            There are more "RS232" serial ports in the world today than there
            ever have been.

            > My main concern though, were the required voltage levels. It seemed
            > that the Seagate drive wanted TTL levels. So it was recommended that
            > the use of an RS232 to TTL adapter be employed. I didn't have one of
            > those, but I did have a USB-to-RS232 adapter. I figured that unless
            > the adapter employed some sort of voltage doubler to get the voltages
            > up to the normal Rs-232 levels, I would be safe with the 5 volt USB
            > power. Well that didn't work. See my overclock post above for more
            > details.

            The problem is that RS232 employs inverted levels, and an RS232 level
            converter performs that inversion. Further, the USB<->serial adapter
            likely DOES include a DC-DC converter to generate higher (but likely not
            very high) voltages than the 5V supplied by USB.

            -Dave

            --
            Dave McGuire, AK4HZ
            New Kensington, PA
          • joshbensadon
            ... Thanks Dave, I was wondering when someone would catch that inverted signal issue. I think there are a number of RS-232 to TTL converter boards
            Message 5 of 12 , Jul 11 2:13 PM
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              --- In midatlanticretro@yahoogroups.com, Dave McGuire <Mcguire@...> wrote:
              >
              > The problem is that RS232 employs inverted levels, and an RS232 level
              > converter performs that inversion. Further, the USB<->serial adapter
              > likely DOES include a DC-DC converter to generate higher (but likely not
              > very high) voltages than the 5V supplied by USB.
              >

              Thanks Dave, I was wondering when someone would catch that "inverted signal" issue. I think there are a number of RS-232 to TTL converter boards available on ebay. Of course you know it's nothing more than a DB-9F and a MAX-232 chip, but it's nice to have it built for you.

              If anyone is interested, I have some blank boards that were made to fit inside a DB-9 shell and provide TTL output, actually they even have a place to install a PIC chip. It's part of a project I did to build a cheap low resolution 4 channel data logger. Funny, it's the same product I was talking about on the SEBHC forum.

              :)J
            • RonK
              Hi Guys, Thanks for all your help. I really did learn alot from your responses, and would like to share the information with others who are trying to
              Message 6 of 12 , Jul 11 4:57 PM
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                Hi Guys,

                Thanks for all your help. I really did learn alot from your responses, and would like to share the information with others who are trying to troubleshoot their broken Seagate drives. There are lots of folks out there who are desperate to resurrect their data.
                I believe the adapters on eBay sell for around $5 which is probably less than the cost of trying to put one together from scratch.

                Regards,
                Ron

                --- In midatlanticretro@yahoogroups.com, joshbensadon <no_reply@...> wrote:
                >
                > --- In midatlanticretro@yahoogroups.com, Dave McGuire <Mcguire@> wrote:
                > >
                > > The problem is that RS232 employs inverted levels, and an RS232 level
                > > converter performs that inversion. Further, the USB<->serial adapter
                > > likely DOES include a DC-DC converter to generate higher (but likely not
                > > very high) voltages than the 5V supplied by USB.
                > >
                >
                > Thanks Dave, I was wondering when someone would catch that "inverted signal" issue. I think there are a number of RS-232 to TTL converter boards available on ebay. Of course you know it's nothing more than a DB-9F and a MAX-232 chip, but it's nice to have it built for you.
                >
                > If anyone is interested, I have some blank boards that were made to fit inside a DB-9 shell and provide TTL output, actually they even have a place to install a PIC chip. It's part of a project I did to build a cheap low resolution 4 channel data logger. Funny, it's the same product I was talking about on the SEBHC forum.
                >
                > :)J
                >
              • Dan Roganti
                ... The interweb has plenty of info out there to help with this. There really isn t any mystery to the interface. After a few min of searching for Seagate
                Message 7 of 12 , Jul 11 4:57 PM
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                  On Thu, Jul 11, 2013 at 11:32 AM, RonK <rkushnier@...> wrote:
                  I thought you guys could appreciate this.

                  I've been trying to "unbrick" a Seagate SATA 750 GB barracuda hard drive. The recommended approach is to go through it's 4-pin jumper connector to reach its serial port. http://www.overclock.net/t/457286/seagate-bricked-firmware-drive-fix-with-pics/240#post_20364127

                   It's "Back to the Basics" of RS232 technology.  Oh no!  Would I really have to open that trapdoor in my brain that I hadn't accessed for thirty years, and pull out all the old stuff? I guess so. Baud rate, Parity, STOP bits, Flow Control- oh all that wonderfulness... here again!


                  The interweb has plenty of info out there to help with this. There really isn't any mystery to the interface. After a few min of searching for Seagate serial port, it clearly defines this to be a TTL level interface. Even the com settings are defined - just pop the settings into your terminal pgm and go. And the RS232 - TTL converters cost only a few bucks. 


                   

                  My main concern though, were the required voltage levels. It seemed that the Seagate drive wanted TTL levels. So it was recommended that the use of an RS232 to TTL adapter be employed. I didn't have one of those, but I did have a USB-to-RS232 adapter. I figured that unless the adapter employed some sort of voltage doubler to get the voltages up to the normal Rs-232 levels, I would be safe with the 5 volt USB power. Well that didn't work.  See my overclock post above for more details.


                  This is where you can find some info about the Seagate serial port being only TTL and addt'l instruction to access the Seagate drive. 

                  The fact that the MAX232 level converters are inverted is a non-issue. This is part of the RS232 standard. A Mark signal, negative level, is a logic "1' and vice versa - this conversion is done transparently in hardware. This is why it's important to use the correct adapter. And why you want a RS232 to TTL adapter  - convert RS232 levels to TTL levels and not the other way around. With the USB to RS232 adapter, you are converting TTL levels ( albeit differential on USB) to RS232 levels - which is the opposite. 

                  As for the RS232 to TTL adapter, you can find them easily online for only $5 and free shipping, even on eB@y

                  And you could even build one with only 2 transistors, a few resistors and a diode.

                  Dan



                • Jeff Jonas
                  ... I m not at home this week so I can t check what parts/boards/assemblies I have but there are many lovely choices - the Adafruit FTDI friend converts TTL
                  Message 8 of 12 , Jul 12 1:01 AM
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                    > This is where you can find some info about the
                    > Seagate serial port being only TTL

                    I'm not at home this week so I can't check what parts/boards/assemblies I have but there are many lovely choices

                    - the Adafruit "FTDI friend" converts TTL serial to USB, so it naturally works with Linux, Windows, OS/X, etc. There are several variations of the FTDI chip board, the most important options being jumpers for power source, 3.3 or 5V serial, and how many signals are available (the FTDI chip offers a lot for handshaking and "bit banging")

                    - there are several MAX232 chips from which to choose. The most basic converts 5V TTL to RS232 using 4 external capacitors. Others allow 3.3V logic and/or no external capacitors. For breadboarding and experimenting, I prefer the pre-assembled postage stamp size boards, available from many sources.

                    --jeff Jonas
                  • joshbensadon
                    ... I recently bought 5 Maxim RS-232 chips from China, very cheap. But I got burned (literally). Those chips had some defects. They would get extremely hot
                    Message 9 of 12 , Jul 12 6:27 AM
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                      --- In midatlanticretro@yahoogroups.com, "Jeff Jonas" <jeff_s_jonas@...> wrote:
                      >
                      > - there are several MAX232 chips from which to choose. The most basic converts 5V TTL to RS232 using 4 external capacitors. Others allow 3.3V logic and/or no external capacitors. For breadboarding and experimenting, I prefer the pre-assembled postage stamp size boards, available from many sources.
                      > --jeff Jonas

                      I recently bought 5 Maxim RS-232 chips from China, very cheap. But I got burned (literally). Those chips had some defects. They would get extremely hot and pop. I tried some Intersil chips from my old (diminishing) stock pile, no problem.

                      :)J
                    • dfnr2
                      ... The *-232A versions are easier to work with and require only 0.1uF caps. New chips from reputable vendors can be had for a little over $1:
                      Message 10 of 12 , Jul 12 7:40 AM
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                        --- In midatlanticretro@yahoogroups.com, joshbensadon <no_reply@...> wrote:

                        > I recently bought 5 Maxim RS-232 chips from China, very cheap. But I got burned (literally). Those chips had some defects. They would get extremely hot and pop. I tried some Intersil chips from my old (diminishing) stock pile, no problem.
                        >
                        > :)J
                        >

                        The "*-232A" versions are easier to work with and require only 0.1uF caps. New chips from reputable vendors can be had for a little over $1:

                        http://www.mouser.com/Semiconductors/Interface-ICs/RS-232-Interface-IC/_/N-45lx1Zscv7?P=1yztkj3Z1z0xwq2Z1yzrawtZ1z0y3waZ1z0z44dZ1z0y33tZ1z0y33vZ1yzspjfZ1z0xuzo&Keyword=232a&FS=True&Ns=Pricing|0

                        Dave
                      • Mike
                        From time to time, those RS232 to TLL adapters come in handy. I use the MAX202 instead of MAX 232, as it is a little easier to deal with. This single sided
                        Message 11 of 12 , Jul 12 8:07 AM
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                          From time to time, those RS232 to TLL adapters come in handy. I use the MAX202 instead of MAX 232, as it is a little easier to deal with.

                          This single sided PCB I designed for the SCELBI does essentially what you need, It does have an extra flipflop needed for the SCELBI TX interface that can be bypassed (leave off the 7474 and jumper pin 9 to 13).

                          http://www.willegal.net/blog/?p=4459

                          I originally did a version of the board without the flip flop, that I used to reprogram a Sony CRT a while back. That is probably exactly what you need, but I don't know where the artwork is, at the moment.

                          One of my PS/2 to ascii keyboard adapters could also be adapted, by leaving off the micro-controller and connecting directly to where the TX and RX pins on the micro-controller would normally be.

                          http://www.willegal.net/appleii/appleii-kb-int.htm

                          If you are familiar with AVR programming, the PS/2 adapter could also be repurposed as a parallel to RS232 converter (paper tape reader?), but that is another story.

                          regards,
                          Mike W.


                          --- In midatlanticretro@yahoogroups.com, joshbensadon <no_reply@...> wrote:
                          >
                          > --- In midatlanticretro@yahoogroups.com, "Jeff Jonas" <jeff_s_jonas@> wrote:
                          > >
                          > > - there are several MAX232 chips from which to choose. The most basic converts 5V TTL to RS232 using 4 external capacitors. Others allow 3.3V logic and/or no external capacitors. For breadboarding and experimenting, I prefer the pre-assembled postage stamp size boards, available from many sources.
                          > > --jeff Jonas
                          >
                          > I recently bought 5 Maxim RS-232 chips from China, very cheap. But I got burned (literally). Those chips had some defects. They would get extremely hot and pop. I tried some Intersil chips from my old (diminishing) stock pile, no problem.
                          >
                          > :)J
                          >
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