TL16C752B
3.3-V DUAL UART WITH 64-BYTE FIFO
SLLS405A – DECEMBER 1999 – REVISED AUGUST 2000
PRINCIPLES OF OPERATION
line status register (LSR)
Table 11 shows line status register bit settings.
Table 11. Line Status Register (LSR) Bit Settings
BIT NO. BIT SETTINGS
0
1
2
3
4
5
6
7
0 = No data in the receive FIFO
1 = At least one character in the RX FIFO
0 = No overrun error
1 = Overrun error has occurred.
0 = No parity error in data being read from RX FIFO
1 = Parity error in data being read from RX FIFO
0 = No framing error in data being read from RX FIFO
1 = Framing error occurred in data being read from RX FIFO (i.e., received data did not have a valid stop bit)
0 = No break condition
1 = A break condition occurred and associated byte is 00. (i.e., RX was low for one character time frame).
0 = Transmit hold register is not empty
1 = Transmit hold register is empty. The processor can now load up to 64 bytes of data into the THR if the TX FIFO is enabled.
0 = Transmitter hold and shift registers are not empty.
1 = Transmitter hold and shift registers are empty.
0 = Normal operation
1 = At least one parity error, framing error or break indication in the receiver FIFO. BIt 7 is cleared when no more errors are present
in the FIFO.
When the LSR is read, LSR[4:2] reflect the error bits [BI, FE, PE] of the character at the top of the RX FIFO (next
character to be read). The LSR[4:2] registers do not physically exist, as the data read from the RX FIFO is output
directly onto the output data-bus, DI[4:2], when the LSR is read. Therefore, errors in a character are identified
by reading the LSR and then reading the RHR.
LSR[7] is set when there is an error anywhere in the RX FIFO and is cleared only when there are no more errors
remaining in the FIFO.
NOTE:
Reading the LSR does not cause an increment of the RX FIFO read pointer. The RX FIFO read
pointer is incremented by reading the RHR.
NOTE:
TI has found that the three error bits (parity, framing, break) may not be updated correctly in the first
read of the LSR when the input clock (Xtal1) is running faster than 36 MHz. However, the second
read is always correct. It is strongly recommended that when using this device with a clock faster
than 36 MHz that the LSR be read twice and only the second read be used for decision making.
All other bits in the LSR are correct on all reads.
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