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Re: Some tests with my Macintosh Centris 650



On Sun, 25 Jan 2015, I wrote:

> 
> I've soldered up mini-DIN8 to DB9 cables in the past but it is fiddly 
> and time consuming. (The Mac serial ports are RS-422 but they become 
> RS-232 compatible by grounding the appropriate pin.) In my experience it 
> is easier to find an old serial printer (aka cross-over) cable: these 
> are male to male, mini-DIN8 to mini-DIN8, DTR to DTR.

Oops. I meant, DTE to DTE, aka "cross-over" or printer cable, as opposed 
to DTE to DCE which would be a modem cable.

-- 

> 
> A lot of low-end Macs were bundled with low-end Apple or HP inkjets, with 
> such a serial cable. An equivalent cable was used with Newtons and 
> QuickTake digital cameras. They are common, and can also be used to create 
> a two-node localtalk network between any two macs.
> 
> The Keyspan adapter, part no. USA-28X is the one I use; it's well 
> supported on every operating system of interest to me. You can find all 
> this gear for sale on ebay.
> 
> But this bug you are chasing looks to be earlier than any serial port 
> output; if your kernel has CONFIG_EARLY_PRINTK enabled, then the screen 
> will be painted black before anything is sent to the serial port. Any 
> character sent to the serial port will be simulataneously painted on the 
> screen in white.
> 
> It looks to me like the bug you are chasing is an early unhandled 
> interrupt, and may be a bootloader bug. If you've already tried unpacking 
> the gzipped kernel, and tried disabling AppleTalk (see Chooser in the 
> Apple menu), then lastly I'd try disabling all extensions (restart with 
> shift key pressed).
> 
> 


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