Best Practices

ASCOM Command Priority

Ensuring the safety of people and equipment is an important aspect of observatory design and operation. A recent example where a relatively unimportant command interrupted a park operation highlighted the need to establish a best practice command hierarchy to ensure that safety related commands complete successfully.

Though not formally required by the specifications, we suggest that device designers classify commands into three categories and implement logic so that commands in a lower category are not allowed to interrupt commands in a higher category. The categories are:

1. Commands that provide safety for both people and equipment
2. Commands that only provide safety for equipment
3. All other commands

The command assignments for categories 1 and 2 are:

• CoverCalibrator.HaltCover
• Dome.AbortSlew
• Focuser.Halt
• Rotator.Halt
• Telescope.AbortSlew

• Common - Set Connected
• Common - Connect
• Common - Disconnect
• Camera.AbortExposure
• Camera.StopExposure
• CoverCalibrator.CloseCover
• CoverCalibrator.CalibratorOff
• Dome.CloseShutter
• Dome.Park
• Telescope.Park