Solution:

In bit-wise enable the driver only drives the data in the SPACE or ON state. It disables the driver in the MARK or OFF state, allowing the pull up and pull down resistors to bring the system into the correct state. This requires the pull ups and pull downs to be installed correctly. Termination is not recommended Our serial cards uses a counter for enabling the driver. It enables it on each SPACE or ON state and then count for 10 bit times before disabling. Since the UART starts each byte with a start bit, the driver is enabled. Most serial data is set up for 8bit, no parity, one stop bit, and one start bit which adds up to 10 bits. So if they send <00> hex the driver will stay enabled through the whole byte. But if they send hex the driver will stay enabled for 10 bit times after the byte is sent, because the counter resets after each SPACE bit, and the last bit is a SPACE bit. This type of Send Data Control is not heavily dependent on the pull up, and pull down resistors. Not recommend if the customer needs a quick turn around (less than 10 bit times).