Date   : Sun, 04 Jan 2015 21:54:42 -0000
From   : jumbos.bazzar@... (Mark Haysman)
Subject: Serial console active at power-on

If your application doesn't need the sound, speech, keyboard or printer 
port, then you can boot the board without the system VIA in place. You'd 
then "need" something bootable, IE a ROM to tell it what to do.

Mark.

-----Original Message----- 
From: J.G.Harston
Sent: Sunday, January 04, 2015 8:53 PM
To: bbc-micro@...
Subject: Re: [BBC-Micro] Serial console active at power-on

Daniel Beardsmore wrote:
> Holding ctrl+shift at power on causes a different behaviour to
> unplugging the keyboard. The former pauses the OS in MODE 7 before
> POST completes, while the latter hangs the machine in what seems to be
> MODE 0 or 3 (the cursor is clearly a lot narrower).

It's in MODE 0. With no keyboard plugged in the MOS "sees" every key
pressed *including* every keyboard link made. Which means it sees the
startup settings (OSBYTE 255) set to zero (MODE 0, Boot, DiskSpeed=0)
*and* sees Ctrl and Shift being pressed. So, it starts up in MODE 0,
then tries to display <newline>"BBC Computer 32K"<newline> and sits
there on the first <newline> waiting for Ctrl+Shift to be unpressed.
Exactly the same as if you manually hold Ctrl+Shift down.

> Holding down as many keys as I can doesn't cause POST to hang

You can - press Ctrl and Shift. That's what's the MOS is seeing - Ctrl
and Shift being held down, permanently.

(Technically, you're not stopping the POST, that has completed ages ago
before the startup gets as far as attempting to display the startup
banner.)

-- 
J.G.Harston - jgh@...      - mdfs.net/jgh


_______________________________________________
bbc-micro mailing list
bbc-micro@...               
http://lists.cloud9.co.uk/mailman/listinfo/bbc-micro