Caple C871i Manual do Utilizador descarregar pdf (Página 436)

Apple II Computer Info

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### Created : Tuesday, November 12, 1996 Modified: Tuesday, November 12, 1996

### File Type: "TEXT" File Creator: "LMAN"

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Path: news.uiowa.edu!news.physics.uiowa.edu!math.ohio-

state.edu!howland.erols.net!newspump.sol.net!news.mindspring.com!L2Co

From: [email protected] (Larry Knight)

Newsgroups: comp.sys.apple2.programmer

Subject: Re: Apple II Email (Network Connections)

Date: Thu, 10 Oct 1996 21:19:08 -0400

Organization: The L2 Company

Lines: 82

Message-ID: <[email protected]>

References: <[email protected]> <[email protected]>

<[email protected]> <[email protected]> <[email protected]>

NNTP-Posting-Host: user-168-121-33-105.dialup.mindspring.com

X-Server-Date: 11 Oct 1996 01:18:32 GMT

X-Newsreader: MacSOUP 2.2b3

OK, I am new to this discussion, and completely ignorant of Apple II hardware,

but I think I can be of some service.

I am a hardware engineer that designs cache cards for Power Macs, and in a

former life spent a little time with LocalTalk issues when I worked for Hayes

(the modem guys).

A few comments/questions:

1: At the physical layer, LocalTalk (or PhoneNet) boxes are little more than

transformers (open one up sometime and look). They allow the RS-422 (NOT

RS-232!) outputs of the Mac serial ports to drive the signal onto the "bus"

which is the two-wire LocalTalk or PhoneNet cabling that is shared by multiple

devices. RS-422 is a "push-pull" differential output and input system which has

superior noise cancellation properties than "single-ended" drive types like

RS-232. Don't worry though, the conversion between RS232 and RS422 is very

simple and cheap.

2: LocalTalk runs at 230,400 bps, and not at any slower speeds. Not only that,

but it is driven by a particular modulation scheme called Manchester II

encoding, and moreover it uses a SYNCHRONOUS protocol (I think it is SDLC, but

don't quote me on that). Basically, to do LocalTalk easily, you pretty much

should use the chip that Apple uses on their motherboards - The SCC (Serial

Communications Controller), or 8530, available commercially from either Zilog

(are they still around??) or AMD (definitely still around!).

3: Does the Super Serial Card have the SCC on it, or just a simple UART? If

anyone has one handy that they can look at, just read the numbers on the largest

chips on the board, and I can probably tell you what kind of communications chip

that they have there. If it is NOT an SCC (just look for "8530" somewhere on the

chip markings), you will have big obstables to overcome in implementing

AppleTalk. If the Super Serial Card DOES have an SCC on it, then you're far

along the path. The only remaining obstable is the proper programming of the

part, etc. (I'm not saying that is trivial, but at least the hardware support is

Apple II Computer Technical Information : Apple II Family Hardware Info

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