This section of the document describes how an application interfaces to the µH Router using the Unix FIFO interface. If you are only interested in using the router, please go directly to the Set Up page.


Backdoors

When µH Router is shared between multiple applications, the client applications should never directly set the keyer setting. This presents a predicament for an application that want, for example to change the polarity of the FSK keying signal, since the FSK Invert flag bit is a bit that is part of the Settings string.

To accommodate these changes, µH Router uses an unused CONTROL packet for the sending "backdoor" commands to the µH Router. These commands are not forwarded to the keyer and are interpreted by the router.

The backdoor commands start with the 0x0F byte and ends with a 0x8F byte. CONTROL sequences in the microHAM Keyer Protocol which start with 0x0F are for responses from the keyer (when the WinKey chip does not respond) and are not used in the command direction.

The byte that follows the initial 0x0F byte determines the type of the command.

Currently, the following commands are implemented

0F 01 LL 8F

Set or clear the FSK Invert bit. If LL is 0, the FSK Invert bit is cleared, otherwise the FSK INvert bit is set.

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