Initial Clock Format

rpi-rgb-led-matrix-master/adapter/active-3/README.md

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+Adapter PCB to support up to 3 panel chains
+===========================================
+
+   * Supports up to three panel chains for newer plus models and
+     Raspberry Pi 2 that have 40 GPIO pins.
+   * Uses HCT245 to level shift signals from 3.3V to 5V and shield
+     the Raspberry Pi GPIOs from overloading.
+   * Open source KiCAD PCB EDA format.
+   * Optional: Pads to power the Pi with 5V, including optional capacitor footprints.
+   * Connector for RxD input (literally the only GPIO pin left) in case you want to
+     make your panel controlled with a serial interface (3.3V logic level).
+   * Provides a way to choose the pinout for different kinds of 64x64 matrixes.
+   * (not very pretty layout, was just lazy and let the auto-router generate the first pass)
+   * BOM:
+     - 4x 74HCT245 or 74AHCT245 in 20-SOIC, 7.5mm package which should make
+     it easy to hand-solder. Make sure to get the variant with the **T**: HC**T** or AHC**T**
+     (there are also HC or AHC, don't use these).
+     - 4x 100nF ceramic capacitor (0805 package)
+     - 1x 10kOhm resistor (0805 package). Not critcial, just a pullup (2.2k .. 15k probably ok).
+     - 3x 16pin IDC (=2x8) male receptible to connect the panels.
+     - 1x 40pin female connector to connect to the RPi.
+     - 1x (optional) 22μF .. 100μF capacitor for 5V rail (either 1206 SMD or
+       radial electrolytic with 2.5mm pitch/6.3mm diameter)
+   * The Gerber FAB files are provided as [active3-rpi-hub75-adapter-fab.zip](./active3-rpi-hub75-adapter-fab.zip)
+
+The board is also [shared on OSH Park][osh-active3] (not affiliated).
+
+![Preview][rendering]
+![Real World][real-world]
+
+Essentially, this is connecting the output pins through level shifting buffers (they
+are operated at 5V, but the HCT series chips accept 3.3V input levels from the Pi). The
+strobe, OE and clock signals are separately buffered for each connector.
+
+![Schematic][schematic]
+
+## Optional
+
+### Power in
+
+The area on the left has 5V/GND input pads, that allow you to power your Raspberry Pi from
+a 5V source ... which you are likely to have as you are powering the LED Matrix. This is often
+more convenient than using the USB connector to power the Pi.
+
+If you do that, there are pads to add a capacitor to smooth the supply - two footprints are
+provided: C5 and C6 for through-hole or surface mount components. The value is not critical;
+I usually use a 22μF/6.3V ceramic capacitor on the C6 pads.
+
+### Choose E-Line for 64x64 panels with 1:32 multiplexing
+
+If you have a 64x64 matrix with 1:32 multiplexing, you need to supply an `E`-address line to it.
+While the Address lines `A` to `D` have fixed positions on the Hub75 connector, there
+seem to be two different ways to connect the `E` address line: it is either on pin 4 or pin 8
+of the connector. So this adapter board provides the flexibility to choose the right pin for
+your matrix.
+
+Look at the back of the matrix or the documentation to find out for your specific board where
+to connect E.
+
+Once you know that, the jumper area in the bottom left of this adapter board allows to choose
+to which pin to connect the E-address line to. The corresponding other pin should be connected
+to GND. Simply solder a wire bridge as indicated below (or use a jumper that you can change later).
+
+If you are not using such 64x64 matrix, you can connect both these pins to GND.
+
+Here are the typical configurations:
+
+No 1:32 64x64: to GND    | E-Line on Pin 4   | E-Line on Pin 8|
+-------------------------|-------------------|----------------
+![][config-default]      |![][config-pin4]   |![][config-pin8]
+
+### Input for serial RxD
+
+If you are not using a 64x64 display that occupies the E-Line, you can use the RxD serial input -
+this might come in handy if you are using the display to be controlled by a serial line. Be aware
+that the input requires 3.3V level, so if you have a RS232, make sure to first adapt the levels.
+
+[rendering]: ../../img/active3-pcb.png
+[config-default]: ../../img/active3-pcb-config-default.png
+[config-pin4]: ../../img/active3-pcb-config-pin4.png
+[config-pin8]: ../../img/active3-pcb-config-pin8.png
+[schematic]: ../../img/active3-schematic.png
+[real-world]: ../../img/three-parallel-panels-soic.jpg
+[osh-active3]: https://oshpark.com/shared_projects/6xAD1VXr