[TUHS] Re: AT&T UNIX PC (7300) Teardown and Restoration

[Clem Cole <clemc@ccc.com>]

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One more thing ... to be fair to Warner: I believe that adding the F/M
version of this: https://www.amazon.com/dp/B082VM3SJG
should create the traditional electro-mechanical version of a true RS-232C
with the board he suggested (and like him I have a few boxes of these
things in my basement).  I just used Amazon for reference, they used to be
sold by most computer stores.
ᐧ
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On Wed, Jan 4, 2023 at 3:48 PM Clem Cole <clemc@ccc.com> wrote:

> Matt - send me an email offline if you need more help.   Warner speaks the
> truth - although he left out some wizardry that has sadly been lost for
> ages.
>
> The first board he offers will create the interface that an IBM PC/AT
> created which was originally not a standard either (eventually EIA back fit
> it, in RS 232-E IIRC, but RS-232 C which is what the UNIX PC's interface
> was defined does not use it].
>
> From your email, it looks like AT&T out a standard Data Terminal Equipment
> (DTE) pinning on the back of that system (which would make sense). That
> means it should be a >>male<< 25 PIN (i.e. male) D style 'B-sized'
> connector with pins 2 (TX), 4 (RTS), 20 (DTR) being driven; and pins 3
> (RX), 5 (CTS), 6 (DSR), 8( DCD), 22 (RI) as inputs.  With Pin 7 being the
> signal reference ground and Pin 1 being the frame ground (often N/C - but
> do not short to 7 on your board)
>
> The signals should swing from +3 volts to up to +30 when assert as a
> spacing time, and  -3 to -30 volts marking time. However, anything over +/-
> 15 volts is unusual, but the interface is required to accept it.
>  Frankly, +/- 9 volts is most likely what you will see with the 1488/1489
> driver pairs which were the preferred chips used in those days.
>
> Amazon does not seem to sell an equiv that spits out real RS-232C using
> the D connector, but rather this PC/AT variant, so you will need to make a
> cable -- the good news is they do sell:
> https://www.amazon.com/Kentek-Female-Serial-RS-232-Adapter/dp/B07KVFM4MS
>
> My suggestion would be to use this on you Mac/WIndows or Linux box:
>
> https://www.amazon.com/Sabrent-Converter-Prolific-Chipset-CB-DB9P/dp/B00IDSM6BW
> connect it to the cable I just mentioned -- at that point your
> Mac/Windows/Linux Box will look like a Proper 'terminal' as the being
> expected then if needed
>
>
> a 25 pin  null modem between it that the 3B1 such as:
> https://www.amazon.com/Monoprice-DB25-Null-Modem-Adaptor/dp/B001VL8RK2 or
> whatever one you need M/M, M/F -- etc...
>
>
>
> On Tue, Jan 3, 2023 at 7:58 PM Warner Losh <imp@bsdimp.com> wrote:
>
>>
>> https://www.amazon.com/NOYITO-Module-Conversion-Arduino-communicates/dp/B07BJJ1T5G
>>
>> is my go-to for when I need a simple one, though something like
>>
>>
>> https://www.amazon.com/NOYITO-Module-Conversion-Arduino-communicates/dp/B07BJJ3TZR
>>
>> might work better for your setup if you just have more of the TTL gear
>> than RS-232 gear (I have way too many old RS-232 cables because I never
>> know when I'll need them again...)
>>
>> Warner
>>
>> On Tue, Jan 3, 2023 at 5:46 PM segaloco <segaloco@protonmail.com> wrote:
>>
>>> Nope, unfortunately I only know as much as is needed to plug into the
>>> GPIO RX/TX/GND working on single boards. I wouldn't be surprised if my
>>> assumption I just run these pins into the D-25 in the right holes is
>>> bunk...but that's how we learn sometimes. Once I move I should be able to
>>> setup a proper work bench where I can tinker on this sort of thing more
>>> intentionally rather than haphazardly. So perhaps a silly question for an
>>> expert but a valid one for me. I'll chase that angle and see if it bears
>>> fruit.
>>>
>>> - Matt G.
>>> ------- Original Message -------
>>> On Tuesday, January 3rd, 2023 at 4:40 PM, Warner Losh <imp@bsdimp.com>
>>> wrote:
>>>
>>>
>>>
>>> On Tue, Jan 3, 2023, 5:30 PM segaloco via TUHS <tuhs@tuhs.org> wrote:
>>>
>>>> I'd love to get my hands on a 3B2 someday, this'll be cool if I can get
>>>> it going but that'd be a much more robust machine.
>>>>
>>>> I'm starting to suspect if there isn't any sort of boot ROM that spits
>>>> out commentary on the UART and that doesn't get flexed until UNIX is up, I
>>>> may not be able to get very far. I referred to
>>>> http://bitsavers.trailing-edge.com/pdf/att/3b1/999-809-010IS_UNIX_PC_Remote_Access_1986.pdf
>>>> for the serial settings and it appears:
>>>>
>>>> 9600 baud, 1 stop bit, no parity, 8 data bits
>>>>
>>>> And the relevant pins
>>>>
>>>> Pin 1 - GND
>>>> Pin 2 - RX
>>>> Pin 3 - TX
>>>> Pin 4 - RTS
>>>> Pin 5 - CTS
>>>> Pin 6 - DSR
>>>> Pin 7 - GND
>>>> Pin 8 - DCD
>>>> Pin 20 - DTR
>>>>
>>>> So I've plugged my USB-TTY GND/RX/TX into the relevant pins and setup
>>>> the necessary tty settings. The manual then suggests if running null modem
>>>> mode to short pin 4 to 5 and then pins 6, 8, and 20 together, presumably
>>>> omitting any need for modem signalling from the remote machine, doing basic
>>>> serial RX/TX. Unfortunately even with all of this bypassing I get nothing
>>>> out of the RS-232 port. What I don't know is if I could even expect
>>>> something or if this is unlikely to bear fruit whether the hardware works
>>>> or not. In any case, if I do get this thing running I'll have a writeup for
>>>> folks afterwards. If not, then hopefully I can figure out something useful
>>>> to do with this thing rather than junking it.
>>>>
>>>
>>> Silly question... did you level shift to RS 232 levels? You likely
>>> did... but if not...
>>>
>>> Warner
>>>
>>> - Matt G.
>>>> ------- Original Message -------
>>>> On Tuesday, January 3rd, 2023 at 3:53 PM, rob@atvetsystems.com <
>>>> rob@atvetsystems.com> wrote:
>>>>
>>>> Hello Matt,
>>>>
>>>> I’ve got one of these in my garage. I bought it about twenty years ago
>>>> as a working system but when I got it home I noticed that the hard disk
>>>> wasn’t connected but at some point I’d like to get it and my 3b2/300
>>>> working.
>>>>
>>>> Regards, Rob.
>>>>
>>>> On 3 Jan 2023, at 23:27, segaloco via TUHS <tuhs@tuhs.org> wrote:
>>>>
>>>> And here are some pictures of the guts.
>>>>
>>>> https://imgur.com/a/E1ioxZl
>>>>
>>>> Various bits inside date this to late 1985. The good news is it at
>>>> least turns on, but that's about as far as I've gotten with it. The display
>>>> never turns on, nor do I hear any sounds indicating it tries to start the
>>>> CRT. The fans kick on and there it stays until I turn it off. I plugged in
>>>> a USB-TTY to pins 2, 3, and 7 (RX/TX/GND) and listened at 9600 baud 8 bit 1
>>>> stop no parity and got nothing. Swapped the RX/TX, still nothing. Of
>>>> course, that's all predicated on the assumption there's something there to
>>>> even interact with. I have little faith that whatever UNIX install was on
>>>> this is extant. Additionally, it didn't come with a keyboard, so if there
>>>> was some futzing with key combos that would trigger some sort of UART over
>>>> those lines, I can't do that. I wonder if there are some contacts inside I
>>>> can just poll for activity with this serial connector, not sure how safe
>>>> that is...
>>>>
>>>> Anywho, the CPU has a bit of corrosion on the surface, not sure how
>>>> that bodes for the innards, but this is in kinda rough shape either way. I
>>>> hope I can salvage it but if not, I'm going to at least do some study on
>>>> the CRT particulars and see if I can extract and keep the monitor from it,
>>>> been wanting a smaller CRT to have around for a while.
>>>>
>>>> - Matt G.
>>>> ------- Original Message -------
>>>> On Tuesday, January 3rd, 2023 at 12:20 PM, segaloco via TUHS <
>>>> tuhs@tuhs.org> wrote:
>>>>
>>>> Good day everyone, just starting a thread for yet another project I'll
>>>> be tinkering on over time. Picked up a (presumably broken/untested) 7300
>>>> off eBay to at the very least tear down and get some good pictures of and,
>>>> with some luck, perhaps get working again.
>>>>
>>>> https://imgur.com/a/CExzebl
>>>>
>>>> Here are some pictures of the exterior for starters. I'll update this
>>>> thread when I've got pictures of the guts and also with any info I can
>>>> glean regarding whether this might be salvageable. The rust on the back is
>>>> pretty nasty but I've seen older/worse start up just fine.
>>>>
>>>> - Matt G.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>

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