20 Jun
2015
20 Jun
'15
10:37 a.m.
I thought of throwing that idea out there, but having lived through the great RAM famine
the thought of a spare
RAM chip seemed kind of silly. Incidentally, the RAMs are all soldered on my Camintonn
boards.
All the RAMs (but not the buffers) on the NatSemi boards are in sockets. And I am not sure
this is a
Good Thing, they are not good quality sockets at all. They're the very cheap ones that
make contact with
one side of the IC pin only. But replacing the lot with turned pin is something I will
only do if I start having
RAM problems on those boards.
I've done a little buzzing out with an ohmmeter :
The green LED + a 270R resistor are across the 5V line (which is presumably the battery
backed memory
supply line. if you have that optio). I assume this indicates the board is powered up.
The moving contact of the switch is grounded.
One of the other contacts of the switch goes to the yellow LED + 270R to +5V. So as
suggested, the yellow
LED indicates the state of the switch.
The other contact goes into the logic. I've not traced it all out yet, but it would
appear to disable many of
the buffers when it is low (i.e. when the yellow LED is off). So the idea that the yellow
LED is on for normal
operation and the switch can turn it off and disable the board makes a lot of sense.
That 'extra' RAM gets power, but nothing else. As far as I can tell none of the
other pins go anywhere. Isn't
that a bad idea, to have a MOS device with all inputs floating? I would have thought it
would have been
better to tie eveything (including the +5V pin) to ground, or to power the RAM but have
pull-up resistors
on all the inputs.
-tony