Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!sun!vector!poynton From: poynton@vector.Sun.COM (Charles A. Poynton) Newsgroups: comp.sys.mac.programmer Subject: Re: How fast can a MAC-SE drive a serial line? Summary: AppleTalk runs at 230.4 kb/s, and hogs the CPU. Message-ID: <96452@sun.Eng.Sun.COM> Date: 29 Mar 89 18:29:36 GMT References: <13655@jumbo.dec.com> <28021@apple.Apple.COM> Sender: news@sun.Eng.Sun.COM Reply-To: poynton@sun.COM (Charles A. Poynton) Organization: Sun Microsystems, Mountain View Lines: 20 The official documentation states that AppleTalk runs at 230.4 kb/s, a nice even multiple of 9600 b/s. Macintosh Family Hardware Reference Manual says that the AppleTalk driver runs the SCC timed with a 3.672 MHz clock, which the SCC divides by 16 to obtain the bit rate. This does not divide out to 230.4 kb/s. I suspect that the figure should be 3.6864 MHz, which is the dot clock of the video circuitry (exactly 15.6672 MHz) divided by four and a quarter. Sorry, I can't help you with the software issues, but as Byron Han points out, AppleTalk communications are not interrupt driven: the AppleTAalk driver takes over the machine. C. ----- Charles A. Poynton Sun Microsystems Inc. 2550 Garcia Avenue, MS 8-04 415-336-7846 Mountain View, CA 94043 -----