Software - ASCOM Focuser Driver/Focuser Firmware
The Beta OnStep ASCOM unified driver (supporting Telescope, Focuser, Rotator, and Switch interfaces) for OnStep release-3.16 and later, is available to download at the ASCOM OnStep Driver page.
Three focuser firmwares exist: OnFocusDC (for DC motors,) OnFocus (for Stepper motor,) and OnStep focuser support.
They use similar commands and one ASCOM driver works with all. More detail on the hardware is here.
The Stable ASCOM driver (version 1.5.7) for OnStep release-3.16, is available to download here.
The prior ASCOM driver (version 1.4.0,) for OnStep release-2.22 and before, is available to download here.
The last version, without OnStep support, is available here.
The latest firmware is available to download from GitHub.
The ASCOM focuser dialog:


Commands across the serial interface are as follows (this command set was designed based on the ASCOM focuser interface documentation):
ASCOM Driver revision history:
Move In | :MIn# | Reply:[none] |
Move Out | :MOn# | Reply:[none] |
Move to Absolute position [OnFocus only] | :MAn# | Reply:[none] |
Info. status M=moving, S=stopped | :IS# | Reply:M# or S# |
Info. Product | :IP# | Reply:On-Focus# |
Info. Number (version) | :IN# | Reply:1.0a1# |
Get full In position | :GI# | Reply:n# |
Get Max out position | :GM# | Reply:n# |
Get Position | :GP# | Reply:n# |
Get power level % [OnFocusDC only] | :GL# | Reply:n# |
Get Scale (microns per step/ms) | :GS# | Reply:n.n# |
Set current position Zero | :SZ# | Reply:[none] |
Set Half travel position [OnFocus only] | :SH# | Reply:[none] |
Set full In position n [OnFocusDC only] | :SIn# | Reply:[none] |
Set Max out position n | :SMn# | Reply:[none] |
Set power level xxx % [OnFocusDC only] | :SLn# | Reply:[none] |
Set PWM frequency 31khz(1), 3.9khz(2), 488hz(3), 122hz(4), 30hz(5) [OnFocusDC only] | :SFn# | Reply:[none] |
v1.5.7 Moved settings to ASCOM profile stores. Normalized version naming.
v1.56 Fix for comms bug.
v1.55 Added support for OnStep TCF.
v1.40 Added support for OnStep DC stepper motors power level control. Added support for Checksumed Comms. More reliable IP Comms.
Here are the older versions of the ASCOM driver and firmware.