How does an Abacus work?
When MIDI Came about in the 1980s, MESA/Boogie embraced this new protocol that allowed electronic musical instruments, computers and other related devices to connect and communicate with one another and created products like the MIDI Quad Preamp, the MIDI Matrix, the TriAxis and came up with Abacus to control program changes of these devices with your foot. We don’t happen to have a manual for an Abacus. It was designed to be pretty intuitive though. In order to communicate with other MIDI device, the Abacus needs to be set to the same MIDI Channel as the rest of your gear (using the Channel Select buttons). Once on the appropriate MIDI Channel it sends Program Change information to whatever MIDI devices are on that same MIDI channel. You can step through program numbers using the Program Select +1 / -1 buttons. You can change banks of Program Numbers in increments of ten with the Program Select -10 / +10 buttons and you can jump to a specific Program Number within a bank of ten by stepping on the numbered button (lit by red LEDs) that corresponds to the second digit of the program you wish to go to. For example if you are currently on program 22 and want to go to program 27, simply step on the button beneath the number 7.
The Abacus has three jacks on its rear panel, a power input jack (12VDC @ 500mA), a 7 pin din / MIDI jack & a locking 4 pin XLR jack (for interlinking with the Mesa MIDI Matrix switcher or MIDI Quad Preamp). You only need a 7 pin din cable if sending power to the Abacus via the footswitch cable. The TriAxis has the ability to allow you to plug your power supply into it and send the power through a 7 pin din cable. If you plug your power supply direct into the Abacus, you only need a 5 pin din cable to broadcast to other MIDI gear. The power Supply should meet the following requirements: 12 Volts @ 500 ma, Tip = Ground and Sleeve = Positive.