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Introducing (and interest check) CircuitTalk: LocalTalk for PowerMac G4

Byte Knight

Well-known member
I got one of the early access boards (got here overnight to the US even!) for my QuickSilver. I wasn't using the internal modem, and I wanted to be able to use a wifi modem with it to connect to BBS's and for testing my own BBS. Installation was a breeze, but I couldn't get ZTerm 1.1b7 (PPC version) to work with it. Interestingly, the 68k version (1.0.1) works just fine and allows you to properly select the gPort serial driver. We're up and BBS'ing!
Picture 6.jpg
 

Nixontheknight

Well-known member
I got one of the early access boards (got here overnight to the US even!) for my QuickSilver. I wasn't using the internal modem, and I wanted to be able to use a wifi modem with it to connect to BBS's and for testing my own BBS. Installation was a breeze, but I couldn't get ZTerm 1.1b7 (PPC version) to work with it. Interestingly, the 68k version (1.0.1) works just fine and allows you to properly select the gPort serial driver. We're up and BBS'ing!
View attachment 39453
Interesting. I’ll have to see if it works with AppleTalk if I ever get sent one for my (currently broken) MDD
 

zefrenchtoon

Well-known member
There is no secondary board. This board replace directly the modem one in the Cube as you can see in the attached installation manual.
 

Attachments

  • CubePort Manual.pdf
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CircuitBored

Well-known member
There is no secondary board. This board replace directly the modem one in the Cube as you can see in the attached installation manual.

Oof, now that is going to be a fun one to clone...

Surprise, surprise, it's a DS8925... :)

It seems that was the only chip that ever got used on these cards for G3s and G4s. I'm not entirely sure why, probably just because they were cheap and plentiful.

The most bizarre thing I've noticed is just how many revisions of these cards there were. The G4 version had four (maybe five) revisions and the G3 had three. Each one has completely different trace routing and for seemingly no good reason.
 

cheesestraws

Well-known member
It seems that was the only chip that ever got used on these cards for G3s and G4s. I'm not entirely sure why, probably just because they were cheap and plentiful.

I looked up the chip, it appears they used it because it was well-optimized for AppleTalk

Yeah, I suspect price and convenience here. There were other suitable chips, like the TI SN75LBC776 which (IIRC) were used by the USB Mac Serial adapters whose name temporarily escapes me, but I don't think there were that many others. Of course, there's nothing special about the transceivers in those chips, you can assemble a Mac serial port driver quite happily out of two ICs (and plenty of 68k Macs did)

But a one-chip design is easier, which is the entire reason these chips existed, and if the National part were cheaper, that might explain its ubiquity here?
 

treellama

Active member
Some images from my early access CircuitTalk in my Sawtooth G4:

Perfect fit where the modem board was. The IDC routes under the motherboard, there’s a little opening right next to the airport card:

tempImage4W2iKc.jpg

Installed in the metal shield the modem jack used to be in. Again there's a convenient place to route the IDC cable on a Sawtooth:

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The view from the back:

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Some notes I have from installing: the screw holes leave a bit of room for alignment, both when putting the board in the modem housing, and when holding the housing to the back of the machine. So at each step I suggest putting a mini DIN-8 cable in to make sure it fits through, then tightening down the screws. I didn't do this the first time and mini DIN 8 cables wouldn't fit in and hold snugly.

tempImage9sPyva.jpgtempImagecAWeRJ.jpg

Once installed, LocalTalk worked great via a printer cable to my Performa. And, zmodem at 21K/sec to my Linux box, using Z-term 1.0.1. I wasn't able to get any speeds higher than 230400 to work, but I'm not sure whether the serial port on the other side supports higher speeds either. My SC-7 serial port isn't working so I couldn't test MIDI, but that and LocalTalk are things the CircuitTalk should be able to do that no USB-serial adapter can.

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CircuitBored

Well-known member
It's time for an update! Here's what's going on in CircuitTalk land:

The new batch of purple G4 PCBs is in but I'm a little disappointed in the silkscreen quality. I've raised an issue with JLC and it seems as though they've had some trouble with their silkscreening process so they will be being remanufactured and shipped out soon-ish. This is not the sort of issue I was anticipating but mistakes happen and this is ultimately not a time-sensitive project.

In other news: the parts for my first run of boards have now all arrived so we are just waiting on the corrected PCBs to appear before I can start shipping these out to people.

Regarding other variants of CircuitTalk:

I have now acquired a Mac Mini G4 (thanks again, @ArmorAlley) so I will soon be prying this thing open and starting to poke around. I'm brainstorming methodologies for ascertaining the modem card's pinout but it'll probably be a mix of looking at the datasheets of the original modem card and probing with an oscilloscope. Perhaps I should invest in a logic analyser...

ArmorAlley also found a spare B&W G3 modem card and I have identified the internal modem connector. I designed a printed connector breakout board so I didn't have to go through the hellish process of building another rats' nest. It would have been nice to have the pads numbered left to right (and in rows of ten) but I just couldn't get the trace routing to work. With all this in hand I am in a good place to start work on the G3 version. According to Alex Hixon the pins on this connector are very similar to the G4 (albeit with thirty extra connections). I have five of these boards so if anyone would like one for their own project please let me know.

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I have also gotten my hands on some PowerBook G3s! I have a Wallstreet and a Pismo at the ready and will be taking a look at the first PowerBook version of CircuitTalk very soon! It's going to be a busy couple of weeks, project-wise.

All things considered I am making much faster progress than I ever expected. At this rate I'll definitely have the G3 and PowerBook versions ready in a couple of months. That said, the Mini version is going to take a lot more time and will quite possibly require a brand new driver.

I will be sure to keep everyone well-updated on developments as they unfold.
 

zefrenchtoon

Well-known member
Great news !

I don't know if you are aware of but, for your information, the Mac Mini G4 modem card (ref 922-6492) is used in many other models of Mac:

eMac – USB 2.0 (Early 2004)
eMac (Mid 2005)
iBook G4 (12-inch, Late 2004)
iBook G4 (12-inch, Mid 2005)
iBook G4 (14-inch, Late 2004)
iBook G4 (14-inch, Mid 2005)
iMac G5 (17-inch, Late 2004)
iMac G5 (20-inch, Late 2004)
iMac G5 ALS (17-inch, Mid 2005)
iMac G5 ALS (20-inch, Mid 2005)
Mac mini (Late 2005)
Power Mac G5 (Early 2005)
Power Mac G5 (Mid 2004)
Power Mac G5 (Late 2004)
PowerBook G4 (12-inch, Late 2003)
PowerBook G4 (12-inch, Early 2005)
 

CircuitBored

Well-known member
I don't know if you are aware of but, for your information, the Mac Mini G4 modem card (ref 922-6492) is used in many other models of Mac:

I was aware that this modem card was in a lot of other Macs but I didn't realise it was that many!

Sadly it looks like the modem is internally connected via USB so I won't be able to use that connector for my serial card but there is a large, unused debugging port beneath where the hard drive is located, which is presumably where I'll find my serial lines. Yet another large connector to identify, probe, and source a supplier for - hooray!
 
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