break out separate section for 2560 encoder.

Home.md

@@ -8,6 +8,7 @@ This wiki will collect technical notes, assembly and configuration guides, tips
 
 [Apple II notes](apple-ii-notes)
 
+[Encoder nodes (2560-based)](encoder-2560-notes)
 <details>
 <summary>Programming the Atmega chips</summary>
 Make sure that the DIV8 flag is OFF (or the chip will run at 1 MHz and you will find the encoder to be very sluggish), and the ISP programming flag is enabled (if you want to be able to program via the ISP header)
@@ -30,5 +31,18 @@ All other fuses disabled.
 </details>
 
 <details><summary>For ATMega2560</summary>
-TO DO
+Extended: 0xFF
+High: 0x99
+Low: 0xE7
+
+This corresponds to the following fuse settings
+
+- Brownout Detection Disabled (Extended byte)
+- JTAGEN (in system programming over JTAG) Enabled (High byte)
+- SPIEN (in system programming over SPI) Enabled (High byte)
+- Boot flash size 4096 ((high byte)
+- Full Swing Oscillator, xtal, fast rise, 4.1 ms startup (low byte)
+
+All other fuses disabled.
+
 </details>

encoder-2560-notes/encoder-2560-notes.md

@@ -0,0 +1,23 @@
+Fuse settings for the ATMega2560:
+
+Extended: 0xFF
+High: 0x99
+Low: 0xE7
+
+This corresponds to the following fuse settings
+
+- Brownout Detection Disabled (Extended byte)
+- JTAGEN (in system programming over JTAG) Enabled (High byte)
+- SPIEN (in system programming over SPI) Enabled (High byte)
+- Boot flash size 4096 ((high byte)
+- Full Swing Oscillator, xtal, fast rise, 4.1 ms startup (low byte)
+
+All other fuses disabled.
+
+Errata:
+
+<details><summary>rev 4.2:</summary>
+The footprints for D1-D16 are supposed to have a shorting jumper trace built in.  For keyboards with a diode installed per-key, these diodes are not installed.  Since the jumpers are not pre-configured, wire jumpers must be installed in the D1-D16 positions for the keyboard to scan correctly.
+
+If you are using a keyboard without any built-in diodes (such as a prefabricated key matrix), then install the diodes D1-D16 (1n914, in4148, or similar) to protect the row-scanning TTL outputs from conflicting logic levels in the event of simultaneous keypresses.  
+</details>