Versions
- Version 3.10+
- Added Support for GRBL 0.9v with PWM Spindle.
- Version 3.00 (4 Axis)
- Enlarged board to add a 4th Axis that can clone the X,Y or Z axis. With a 4th option to use pin D12-13 to control it.(Setting up the 4th Axis)
- Added a breakout header for all the Axis’s.
- Added a communication header for UART(Serail) and I2C.
- Added the a connector for an optional fuse.(Fuse not supplies as it needs to be selected for the current that will be used.)
- Capacitors are mounted horizontally giving more clearance between them and the stepper drivers. Good for ventilation.
- Added a pull-up resistor on the axis enable pins. This prevents the pin from being in a floating state.
- Added 2 mounting holes
- Version 2.02 (3 Axis)
- Fixed High Voltage label
- Removed Diode D1.
- Reduced the number of Via’s.
- Version 2.01
- Added a 5V Breakout
- Filled in both sides with Ground Copper
- Moved RX/TX pins to the side so that 26-Pin header can be used. Same as the headers on a Raspberry Pi.
- Small Text Changes
- Version 2.00
- First official version of the CNC Shield.
- All pins used by GRBL has been broken out.
やっとボード開発者の考えがわかりました。
Ver3.00 の Changelog で
Added a pull-up resistor on the axis enable pins. This prevents the pin from being in a floating state.
軸イネーブルピンにプルアップ抵抗を追加しました。 これにより、ピンがフローティング状態になるのを防ぎます。（Google翻訳）
の記載があります。これから推測すると、morih さんの提示された
を意図してのプルアップ抵抗だったようです。
STEPPERS_DISABLE_PIN を EN に電気的に接続しない場合はプルアップ抵抗が意味を持つと考えられますが、接続する場合 floating state 対策は不要であり、従ってこの抵抗も不要と判断します。
STEPPERS_DISABLE_PIN から High が来ている時点で pull-up resistor と役割が被っています。