Sega Master System / Mark III / Game Gear
The address lines point to a memory location inside the cartridge ROM (or RAM). 16 bits are available for addressing (giving a total of 65536 memory locations, or 64 kilobytes), so we need 16 address lines. The address lines are driven by the 4040 counter chips.
We also need to connect a few more links for other cartridge signals, such as Read (RD), and Write (WR).
Solder in the following wire links:
Cut tracks at the following holes:
In order to reduce "clutter" on the board, we can make some of our links on the track side of the Veroboard. This is somewhat more tricky than the usual method, and involves soldering directly to socket or component pins.
Cut the wire to the exact length required and strip only a couple of millimetres or so of insulation from the ends. Mount the wire firmly in place using Blu-Tack, making absolutely sure that the exposed ends are not bridging adjacent pins, then solder them.
Here is an example of such a link:
and here are the links you have to make.
Here's what the SMSReader should look like now: