An idea: TCP/IP to serial bridge (modem emulator)

[porter]

A router can be anything with multiple network interfaces, those interfaces don't have to be of the same type.

So a box with one wireless and one ethernet interface is still a router.

Similarly a box with one ethernet and one serial port can be a router.

There are plenty of embedded PC or microcontroller boards which can implement that.

 

[Bunsen]

II2II: your mission should you choose to accept it is to find a microcontroller with ethernet, TCP/IP and a 230kbps (RS-422?) serial port for under $50 and port an Appletalk stack to it.

I know there's a TCP/IP stack for PICs, there's almost certainly one for AVRs, and it's possible you could fake up a Localtalk port by bit banging.

Personally I don't think the Appletalk to ethernet converters are all that hard to find. The Farallon ones are nice, as they can use the full 230kbps.

Regarding serial ports on OpenWRT routers - I was having a look at that page last night and it seems on most of them it involves soldering a connection to the onboard ISP (in system programming) port. In other words, there is a serial port onboard, but it's not exposed to the outside world via the case. It doesn't look difficult, and there are already software packages to make it useful

You can happily plug a compact mac with MacPPP into a / UNIX server running PPPD, only cost is a normal mac serial cable, but you are limited to RS/232 speeds.

I used to do just that when I was living with Linux nerds, and my 6100 didn't have an AAUI converter

 

[equant]

But how would that work *physically* ??? How do you connect a compact Mac to a router?

Very many routers (and yes, I'm talking about the kind you buy at Home Depot) out there have serial ports *inside* them (note J6 and J7 are both serial ports)....

http://devices.natetrue.com/musicap/12%20-%20Serial%20ports.jpg'>http://devices.natetrue.com/musicap/12%20-%20Serial%20ports.jpg

That's from (http://devices.natetrue.com/musicap/) a wireless music player built out of a router. It gives you an idea of the fun that can be had.

Here's alink to the OpenWRT hardware comapatibility guide which specifies the routers with serial ports...

http://wiki.openwrt.org/TableOfHardware?action=show&redirect=toh

It's not a plug and play solution, but potentially a very satisfying solution if you're into hacking around. I've thought about doing it with a wireless printserver/router that already gets used as a wireless bridge for ethernet enabled classic macs, but alas, it's not openwrt worthy.

Anyway, I know this isn't exactly what anyone wanted, and I didn't mean to hijack the thread, but I figured I should explain fully.

 

[II2II]

equant:

Of course people will want to know about your solution. It's certainly applicable in a case like this since a lot of people are going to have a router.

Will it work well in this configuration? I don't know. I took a quick look at my router and it is supported by OpenWRT. Sweet. I have yet to figure out how to add a serial port, but there are a couple of jumper blocks that may serve that purpose. If so that would be fantastic: no soldering.

Still, there may be one hitch. A lot of these ports, particularly the user added ones, are probably going to lack hardware flow control. This may make the link a bit less reliable. But hopefully not.

 

[porter]

230kbps (RS-422?) serial port

Alas, they are *very* different beasts.

LocalTalk uses HDLC framing with special bit encoding to allow clock recovery, tri-state drivers followed by an isolation transformer.

The Zilog SCC does all of that encoding/decoding except for the tri-state driver and transformers.

There used to be LocalTalk ISA boards available from a few manufacturers.

 

[Bunsen]

So are these Zilog SCCs obtainable?

 

[porter]

So are these Zilog SCCs obtainable?

Yes....

http://en.wikipedia.org/wiki/Zilog_SCC

http://www.zilog.com/products/partdetails.asp?id=Z85C30

 

[Bunsen]

230kbps (RS-422?) serial port

Alas, they are *very* different beasts.

LocalTalk uses HDLC framing with special bit encoding to allow clock recovery / The Zilog SCC does all of that encoding/decoding except for the tri-state driver and transformers.

I had to resort to the 'pedia for clarification:

/ expensive multi-mode (RS-232/RS-422) capable serial ports. The port was driven by the Zilog SCC which could serve as either a standard UART or handle the much more complicated HDLC protocol which was a packet oriented protocol which incorporated addressing, bit-stuffing, and packet checksumming in hardware. Coupled together with the RS422 electrical connections /

I always gets my layers confuzzled. So physically/electrically the port is both RS-232 and 422 compatible, and HDLC runs on top of the RS-422 mode?

http://en.wikipedia.org/wiki/High-Level_Data_Link_Control

But anyway, I gather your point is that the Zilog controller & associated hardware handles all the physical and data link layer stuff, and it would be far simpler to just use one than try to emulate it in code on a micro.

A quick check at octopart confirms widespread availability of the SCC

 

[porter]

I always gets my confuzzled. So physically/electrically the port is both RS-232 and 422 compatible, and HDLC runs on top of the RS-422 mode?

No, RS232/422 are point to point links. LocalTalk is run on a bus, where tristate drivers are used to disable output when not transmitting.

The following is the guide for AppleTalk including LocalTalk.

http://developer.apple.com/MacOs/opentransport/docs/dev/Inside_AppleTalk.pdf

 

[Bunsen]

So the recipe looks like this?

Macintosh serial port

:

:

Tristate drivers & transformers

|

Zilog SCC

|

Microcontroller

|

Ethernet MAC

:

:

LAN

 

[porter]

Plus a load of software.

And where would you find all of the components?

(a) in an old mac with ethernet

( B) AsantePrint

 

[luddite]

(a) in an old mac with ethernet

How convenient!

 

[Bunsen]

And depending on the micro, the Ethernet MAC would be built in.

 

[Charlieman]

You don't really have "TCP/IP to serial bridges".

Sorry to come to this thread so late. Surely we do have TCP/IP to serial bridges?

TCP/IP follows the ISO layer standards. Serial comms (RS-232 and RS-422) follow earlier monloithic standards. A bridge is therefore necessary for the two different standards to communicate. Typical application of a TCP/IP to serial bridge is to connect old display signs (programmable via serial) to a modern network.

Alas they don't help with this problem.

 

[Charlieman]

At this point, I don't know how these bridges are wrapping data so I don't know if they will be useful.

For the record, and it may be of help to some of the Apple II folks. With a TCP/IP to serial bridge, you have a set of libraries on the TCP/IP connected host which capture commands to a virtual serial port (sent as if you were using a VT terminal etc) and encapsulate them in TCP. I've seen device specs that list Linux and Windows support, but not Mac OS X or earlier. The TCP packets whizz along the network to the bridge, which assembles them into the right order, and then translates them back into serial.

And it obviously works in the opposite way.

From this we can assume that the bridges have some cache in order to re-order out of sync TCP packets. Probably enough to cope with out of sync TCP packets emulating a 9600bps connection, but not 230kbps.