SERDATR

         This address reads data from a recive data buffer.
         Data in this buffer is loaded from a receiving shift
         register whenever it is full. Several interrupt request
         bits are also read at this address, along with the data as
         shown below.


         +------+----------+--------------------------------------------+
         | BIT# | FUNCTION | DESCRIPTION                                |
         +------+----------+--------------------------------------------+
         | 15   | OVRUN    | Serial port receiver overrun               |
         | 14   | RBF      | Serial port receive buffer full (mirror)   |
         | 13   | TBE      | Serial port transmit buffer empty (mirror) |
         | 12   | TSRE     | Serial port transmit shift reg. empty      |
         | 11   | RXD      | RXD pin receives UART serial data for      |
         |      |          | direct bit test by the micro.              |
         | 10   | X        | Not used.                                  |
         | 09   | STP      | Stop bit                                   |
         | 08   | STP-DB8  | Stop bit if LONG, data bit if not.         |
         | 07   | DB7      | Data bit.                                  |
         | 06   | DB6      | Data bit.                                  |
         | 05   | DB5      | Data bit.                                  |
         | 04   | DB4      | Data bit.                                  |
         | 03   | DB3      | Data bit.                                  |
         | 02   | DB2      | Data bit.                                  |
         | 01   | DB1      | Data bit.                                  |
         | 00   | DB0      | Data bit.                                  |
         +------+----------+--------------------------------------------+