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Comment by fsckin | Hacker News Reader

Mac Plus has a CPU limited line speed of ~19 kilobits/sec? That's pretty amazing.

My first was a Kaypro II with 64kb of RAM, 191kB floppy drive, and a 2.5MHz Z80. I just looked up some videos of them running and the memories came flooding back. Good times.

Just imagine what computing power we'll have in another couple of decades and how silly what we have right now will seem.

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I remember being absolutely devastated when the U.S. Robotics 28.8k modem I purchased was too fast for the 9.6kb/sec speed the 8250 UART on my 386sx. I had to sell it to somebody else and find an expensive internal model with its own UART. I think later they started selling internal modems without UARTS that just used the CPU to do the work, I wouldn't be surprised if that was the case here.

It happened to me with a graphics card regarding PCI bus speed.

Why didn't you just get a new serial board with the 16550A UART?

It's been, many years...IIR the serial port was built into the motherboard.

He's saying get an _extra_ serial board (put it into an ISA slot) that has the 16550 on it. Back then, this was a common way to get around what you're talking about.

Yes, he needs to go back in time and commit nerd seppuku. This is intolerable.

Oh yes. Right. I had forgotten about those. I may have just thought it was simpler to just get an internal modem. Who knows?

It seems like his particular setup is the limiting factor. He should have no problems with 56k rs-232 wih proper cabling. The mac had a dedicated serial controller used for rs-232 and rs-422.

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

LocalTalk wasn't speedy and we were pretty thrilled when we got macs that could support 10/t ethernet, but there was a distinct charm to LocalTalk. (like, the terminators for the cabling consisting of a resistor sticking out of an rj-11 jack!)

I still have a few Dayna Ethernet to LocalTalk bridges I the garage...

According to that article, the fastest widely-supported RS232 speed that chip can communicate at is 19.2 kbit/s - the onboard clock generator simply doesn't support any of the standard speeds above that.

In that case you get yourself a USB to serial dongle which includes a CP210x or a FT232 chipset. Those can be configured to support a huge range of non-standard baud-rates easily.

Linux CP210x method described in http://bb.osmocom.org/trac/wiki/Hardware/CP210xTutorial

FTDI application note on non-standard baudrates: http://www.ftdichip.com/Documents/AppNotes/AN232B-05_BaudRat...

You need an external clock to get a higher bit rate, such as LocalTalk's 230.4Kbps.

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