For more information about the different types of outputs, see the tech guide pages.
Every multiplexer that is used for output is connected to the system bus and uses all 4 address lines, the "SIG" line and 2 power lines (+5v and GND).
The "EN" signal of each output extension board is connected directly to the pin assigned for this OUTPUT extension.
Also, "D" and "L" control lines are used for output devices connected to the extension outputs - 7-segment displays, LED drivers, PWM driver, steppers (only D).
To extend number of 7-segment displays or serial LEDs annunciators that are located in some part of your cockpit, but you don't need more than 8 outputs, you can use 8-channel 74HC4051 multiplexer breakout board.
Note: if you use the 8-bit multiplexer board you should take care about the signal inputs location - it is slightly different from 74HC4067. All bus lines are used the same way as for 74HC4067, except of one address line S3 - it's not used in 8-channel multiplexer.
The single LED can be connected to the main controller board directly, without using the DM13A LED drivers. You can use this if you have a very simple annunciator panel with a few LEDs.
Each serial LED driver (16 LEDs on the DM13A driver or registers) should be connected to the main controller board directly, without using extension boards (MUX).
1. You can configure up to 15 PWM controlled devices connected directly to one of these mega2560 controller pins - 2 to 13 and 44,45,46.
2. You can use 24-channle PWM-controller (TLC5947) connected (CLK signal of the controller) to one of these mega2560 controller pins - 30 ... 39.