SUMMARY: How to get serial port speeds above 38400

From: David Lawrence Oppenheimer (davido@davido.remote.Princeton.EDU)
Date: Sun Jun 19 1994 - 18:41:45 CDT

Thanks to those who responded to my question, which was the following. I am
using a Sun SS5 and SunOS 4.1.3_U1 and need to communicate with an Apple
LaserWriter Select 310 connected to my Sun serial port (this is a PostScript
but non-AppleTalk printer). The problem is that the LaserWriter expects
communication at 57600 baud and I could not figure out how to get my Sun to
communicate through the serial port at speeds higher than 38400 baud. Here is
a digest of the responses I received:



Date: Sun, 19 Jun 1994 12:03:05 -0400 From: Tarl Neustaedter <> To: davido@mindbender (David Lawrence Oppenheimer) Subject: Re: Q: How to get serial port speeds above 38400 on a Sun?

In article <1994Jun18.231800.16948@Princeton.EDU>, you write: > The printer documentation states that the serial port on this > printer uses 57600 baud. But it seems that the maximum serial port speed on > the Sun is 38400--when I try to set br#57600 in /etc/remote, tip complains > that a speed of 57600 is not allowed.

Yikes. The SS5 is not physically capable of doing 57.6kb. The clock rate being fed into the 8530 is 4.9152MHz, and the 8530 divides that down by 32 before feeding it into the baud rate generator. That means the baud rates the SS5 will do are integer divisors of 153.6kb; 76.8 and 38.4 are the obvious rates.

As I recall, 4.1.3_U1 does not support 76.8, since that would involve an interrupt every 100uS, and a maximum latency before losing (incoming) data of less than 300uS. For outgoing data, you might be able to get away with that baud rate; If you'd like, I can investigate what you would have to patch in your kernel to make it work (and at the same time verify the above numbers which are recalled from memory).

An alternative is to buy an SBus card that will perform higher baud rates. I've never looked up the prices, but they shouldn't be too expensive.

As for the generic issue, which comes up periodically on this group, Sun is well aware that people want to use the serial ports at higher baud rates than 38.4; My job right now is to fix this problem in our future workstations (it's going to require different uarts, so won't be retrofittable)


Date: Sun, 19 Jun 1994 01:31:43 -0400 From: Gary Merinstein <> To: davido@mindbender Subject: Re: Q: How to get serial port speeds above 38400 on a Sun?

there are third-party high speed serial port boards available for sparcs. one i'm particularly partial to is called "aurora". i've used it to build a live market data line-feed handler for real-time knight-ridder stock market data feeds, with a 10/40.

you also want to be concerned about async. vs syncronous port speeds: the max. numbers on suns vary depending upon which type you need.


Date: Sun, 19 Jun 94 03:42:00 PDT From: (Syed Zaeem Hosain) To: davido@Princeton.EDU Subject: Re: Q: How to get serial port speeds above 38400 on a Sun? (for printing) The standard Sun serial port cannot be run at 57600 bps - the max is 38400. Some kernel mods allow 76800, but this is unstable in my opinion.

You need an add-on SBUS serial card of some sort, or a parallel port to a printer that has a parallel connector.

Magma Corp (in the 619 area code in San Diego, CA) makes such Sbus cards (I use their 2 Serial/1Parallel card with great results upto 115200 bps serial rates) - I don't know if they have been qualified for the SS5 yet. Give them a buzz and ask.

Finally, keep in mind that PostScript imaging and interpretation speeds are pretty slow to begin with - you *may* not see a tremendous gain in speed when going to faster serial or parallel rates (of course, this is *very* dependent on what you are printing - text file print times will be improved).


Date: Sun, 19 Jun 94 09:25:06 PDT From: (Celeste Stokely) To: davido@mindbender

You can't reliably use serial port speeds above 38400 on Sun serial ports. Sure, you could hack the kernel and get it to work under some circumstances, but the key word is "reliable.

Spend $200 and get an sbus serial-port card that offers the features you're looking for.


Many thanks for the responses.

David Oppenheimer davido@Princeton.EDU

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