When the physical device driver is enabled for this mode of operation, it stops sending data to the transmit hardware when an XOFF is received, and resumes sending data to the transmit hardware when an XON is received.

If this mode is enabled, Error Alerts can be generated when the OS/2 Logging Facility is enabled. If an external device sends an XOFF, but does not send an XON, transmission of data is blocked because the device driver is waiting for the XON to be received. If the XON is not received before the Write Timeout period expires, an Error Alert is generated.

Initial Value

Automatic Transmit Flow Control is disabled.
First Level Open
There is no effect on whether the physical device driver is enabled or disabled for this mode of operation. The state of the physical device driver is reset to show that it has not received an XOFF, so it can transmit (due to automatic transmit flow control), if it is enabled for this mode of operation.
Mode Utility
User interface to enable/disable this mode of the physical device driver.
Automatic Override
When Automatic Transmit Flow Control is enabled, the physical device driver responds to receiving the XOFF within a single character time. That is, Automatic Protocol Override controls the Extended Hardware Buffering capability so that only one character is buffered for transmit at a time, and the device generates an interrupt for every character received (Receive Trigger Level is set to 1).

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