Date   : Sat, 24 Jul 2010 17:09:46 +0100
From   : jgh@... (J.G.Harston)
Subject: Proposed allocation: Configuration RAM byte 8

Proposal to use Configuration byte 8, bit 6-7
See also http://beebwiki.jonripley.com/CMOS_configuration_RAM_allocation

I am thinking of using two bits of configuration RAM to store a default
MIDI parameter. Looking at the list, byte 8, bits 6-7 would be suitable.
Edit uses byte 8 to store its settings in b0-b5. I've checked Edit and it
always leaves bits it's not modifying untouched, so b6-b7 are not modified
by it. Has anybody else used byte 8 bits 6-7?

Specifics:
Most BBC MIDI interfaces (see http://mdfs.net/Info/Comp/BBC/MIDI) use a
6850 ACIA. This requires a clock input. Some interfaces (eg JGH, ETI, M2000)
derive this clock from the BBC's 1MHz signal, and so require the feed-in
clock to be divided by 16 to get the MIDI 31.125KHz clock. Some interfaces
(eg EMR) have an on-board 2MHz clock, so need to divide by 64. I was thinking
of tweeking my *MIDI command to be able to set the appropriate clock according
to stored configuration.

-- 
J.G.Harston - jgh@...