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

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/B00IDS… 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 &lt;imp(a)bsdimp.com&gt; wrote: > > https://www.amazon.com/NOYITO-Module-Conversion-Arduino-communicates/dp/B07… > > is my go-to for when I need a simple one, though something like > > > https://www.amazon.com/NOYITO-Module-Conversion-Arduino-communicates/dp/B07… > > 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 &lt;segaloco(a)protonmail.com&gt; 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 &lt;imp(a)bsdimp.com&gt; >> wrote: >> >> >> >> On Tue, Jan 3, 2023, 5:30 PM segaloco via TUHS &lt;tuhs(a)tuhs.org&gt; 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… >>> 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(a)atvetsystems.com < >>> rob(a)atvetsystems.com&gt; 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 &lt;tuhs(a)tuhs.org&gt; 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(a)tuhs.org&gt; 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. >>> >>> >>> >>> >>> >>