ASYNC_SETMODEMCTRL (46h) - Modem Control Signals ON Mask

Modem Control Signals ON Mask

The physical device driver sets the modem control signals as defined in this field. Bit 0 is DTR; bit 1 is RTS. If any other bits are set/reset by the masks, then a general failure error results. The OFF mask contains a mask (with all bits equal to 0) to turn the modem control signal off. The ON mask contains a mask (with all bits equal to 1) to turn the modem control signal on. If the Parameter Packet indicates both turn off and turn on on the same bit, the bit will be turned on.

For example:

┌─────────┬───────────┬───────────────┐
│Mask ON  │Mask OFF   │Description    │
├─────────┼───────────┼───────────────┤
│   01h   │   FFh     │Set DTR        │
├─────────┼───────────┼───────────────┤
│   00h   │   FEh     │Clear DTR      │
├─────────┼───────────┼───────────────┤
│   02h   │   FFh     │Set RTS        │
├─────────┼───────────┼───────────────┤
│   00h   │   FDh     │Clear RTS      │
├─────────┼───────────┼───────────────┤
│   03h   │   FFh     │Set DTR and RTS│
├─────────┼───────────┼───────────────┤
│   00h   │   FCh     │Clear DTR and  │
│         │           │RTS            │
└─────────┴───────────┴───────────────┘

If DTR Control mode input handshaking, RTS Control mode input handshaking or toggling on transmit is set, then this request cannot try to change the state of the modem control signals, that are being used for input handshaking or toggling on transmit. If the request tries to modify a modem control signal that is being used for input handshaking or toggling on transmit, a general failure error results.

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