[31:8] |
- |
Reserved |
R |
0x0 |
[7:0] |
rbr_thr_dll |
- Receive Buffer Register:
This register contains the data byte received on the serial input port (sin). The data in this register is valid only if the Data Ready (LSR[0] is set to 1). If FIFOs are disabled (FCR[0] is cleared to 0) the data in the RBR must be read before the next data arrives, otherwise it will be overwritten, resulting in an overrun error. If FIFOs are enabled (FCR[0] set to 1) this register accesses the head of the receive FIFO. If the receive FIFO is full, and this register is not read before the next data character arrives, then the data already in the FIFO will be preserved but any incoming data will be lost. An overrun error will also occur.
- Transmit Holding Register:
This register contains data to be transmitted on the serial output port (sout). Data should only be written to the THR when the THR Empty bit (LSR[5] is set to 1). If FIFOs are disabled (FCR[0] is set to 0) and THRE is set to 1, writing a single character to the THR clears the THRE. Any additional writes to the THR before the THRE is set again causes the THR data to be overwritten. If FIFO's are enabled (FCR[0] is set to 1) and THRE is set, the FIFO can be filled up to a pre-configured depth (FIFO_DEPTH). Any attempt to write data when the FIFO is full results in the write data being lost.
- Divisor Latch Low:
This register makes up the lower 8-bits of a 16-bit, Read/write, Divisor Latch register that contains the baud rate divisor for the UART. This register may only be accessed when the DLAB bit (LCR[7] is set to 1). The output baud rate is equal to the system clock (clk) frequency divided by sixteen times the value of the baud rate divisor, as follows: baud rate = (system clock freq) / (16 * divisor)
Note: With the Divisor Latch Registers (DLL and DLH) set to zero, the baud clock is disabled and no serial communications will occur. Also, once the DLL is set, at least 8 system clock cycles should be allowed to pass before transmitting or receiving data.
|
RW |
0x00 |