Serial Communications (16C452)
SERIAL REGISTERS
This section describes the individual UART registers.
You may access or control any of the serial registers summarized in
Table 8-3 on page 8-18. The registers are used to control the serial
ports’ operation and to transmit or receive data. There is a complete
set of these registers for each UART.
The base I/O address of each UART is 03F8h for serial port 1
(COM1) and 02F8h for serial port 2 (COM2). The offset of each
register from the base is shown in Table 8-3 on pages 8-18 and 8-19
and in the "I/O Port Assignments" table on page 8-17.
Note that the state of the Divisor Latch Access Bit (DLAB), which is
the most significant bit of the Line Control register, affects the
selection of certain UART registers. (See page 8-23 for a full
description.) DLAB is reset low when the ZT 8809A is reset or
powered up; the DLAB must be set high by the system software to
access the baud rate generator divisor latches, and reset low again to
access the remaining UART registers.
8-16
