13.22.5 Auto-Baud Function

The MOSFET Gate Driver provides an auto-baud feature that allows the host dsPIC DSC, communicating on the DE2 communications interconnect, to determine the actual baud rate being used by the MOSFET Gate Driver. The feature allows the host to request a 0x55 byte transmission from the MOSFET Gate Driver. The host then determines the MOSFET Gate Driver baud rate and adjusts the host internal Baud Rate Generator (BRG) to match the MOSFET Gate Driver baud rate.

The DE2 pin is used to trigger the auto-baud feature. The host sets the DE2 signal to a logic low for a period of time (auto-baud Break window) that ranges between 1.29 ms and 2.0 ms. The host then releases the DE2 pin back to the host UART control. The host UART then raises the DE2 pin to a logic high value. The MOSFET Gate Driver will respond with a standard NACK (‘0b00nnnnnn’, where ‘nnnnnn’ are the six Least Significant bits (LSbs) received) if the DE2 link was held low for less than 1.29 ms and the byte was not interpreted as a valid command. The MOSFET Gate Driver will ignore the current message if the DE2 link is held low for more than 2.0 ms.

If the driver receives a valid auto-baud request in the allotted time frame, the driver will enter an Auto-Baud state, indicating an auto-baud message has been requested. When the auto-baud function is activated, the DE2 subsystem will disable sending all unsolicited messages to the host.

If the internal Auto-Baud state is set, the driver will wait for a minimum of 0.86 ms and a maximum of 1.19 ms. After the wait time has expired, a 0x55 data byte will be immediately sent on the DE2 link by the driver.

The driver will wait 2.00 ms after sending the 0x55 baud rate data over the DE2 link before transmitting any other messages. The driver will then exit the Auto-Baud state and resume normal DE2 operations. The 2.00 ms wait is needed to allow the host to complete the auto-baud verification and update the host UART Baud Rate Generator.

The MOSFET Gate Driver will always monitor the DE2 link for a logic low before attempting to transmit.

The MOSFET Gate Driver will preempt all DE2 communications upon receiving a logic low on the DE2 link which lasts longer than ten bit times at 9600 baud (Break sequence).

The MOSFET Gate Driver will wait for a period up to 2 ms for the DE2 link to change to a Logic High state after the initial detection of a logic low on the DE2 link. If the DE2 link fails to rise to a logic high level within 2 ms of the initial logic low level, the auto-baud message will be canceled and no message will be sent. The auto-baud function will then be complete.

The driver will send any pending unsolicited messages after the auto-baud function has finished.