Hardware Schemes
edited by Cyrion(sorry, no really schematics this time)

1. HLT
If you want to take some nice screenshots with your camera, or just want to
look at a great graphics, if you are disturbed by your family or the
telephone, this is the right solution for you: _HLT. (HaLT)
The 680xx family of microprozessor has a unique feature, the _HLT-pin. If
this pin is connected to Vcc, +5V normaly, or runs open the prozessor works
as usual. But if you connect it to logic ground GND, the prozessor will
finish its current command cycle, empty his queue and go in the tri-state
waiting cycle. This means, the prozessor disposes himselfs from the adress
and databusses and waits until the HLT-signal resets to Vcc. If so, the
680xx tries to get the bus and reloads his queue, then he starts the work
again. Since the Amiga offers differnt coprozessors for sound and graphics
and does the dram-refresh by himself, the picture and ram-contents will be
still displayed and refreshed even if the main prozessor is in the HLT.
But now, How to do?
You may connect the _HLT-pin in some ways to GND:
a: solder a wire directly on PIN 17 on the prozessor and connect it to a
   GND wire. (be carefull)
b: Use a socket between cpu and mainboard to connect PIN 17(_HLT) to
   ground.(this is most recommended)
c: Connect PIN 55 (_HLT) of the ExpansionPort to PIN 49(GND).Donīt solder
   directly to the mainboard, use a feature-connector instead. (expensive)

I recommend, that you install a LED for the status of you switch, couse if
you prozessor is halted during the boot-phase, the Amiga will not do
anything!

2. EXRAM
Old, but many people still donīt know about this feature in the A500:
During startup, Gary tests the Pin 32(_EXRAM) of the internal
MemoryExpansion Slot CNX(also Pin 32(_EXRAM)) of a connection to ground. If
so, he uses the expansion ram(Slow Ram), otherwise it is left out and you
have only you chipram and optional external ram. The realtime clock is not
affected by this, all programs will find the right time.
I recommend, that you search for the GND-connection of CNX-PIN 32(_EXRAM)
on you ram-expansion board and cut it open, then solder two wires to this
places and use a switch, also a status LED is useful for this switch.

3. PowerSupply
The PowerSupply of the Amiga A500 is not the strongest, so if you want to
connect some HardDisks, Floppies and Ramboxes to you computer, it might
give up. Solution is done in two ways:
a: Buy a new PowerSupply. A very good and affordable one is the following:
   50W, 5V/5.0A, 12V/2.5A, and -12V/0.5A
   available at LACOM Computer&Music, Emscherstr. 45, 4200 Oberhausen 1,
   0208/655051 at the price of 99DM.
   The Power may be even enought to get rid of the extra Supply of your
   harddisk.
b: Use a CMOS-microprozessor 68HC0xx, it will cost about 40DM and will
   reduce the power consuption about 300mA. This may be enough for one of
   the modern 2MB-Ram boxes and four floppies.

4. In one of the next Issues i try to include my schematics of the A500 and
maybe some of the A2000B1-board.