TL16C752B
3.3-V DUAL UART WITH 64-BYTE FIFO
SLLS405A – DECEMBER 1999 – REVISED AUGUST 2000
PRINCIPLES OF OPERATION
receiver holding register (RHR)
The receiver section consists of the receiver holding register (RHR) and the receiver shift register (RSR). The
RHRisactuallya64-byteFIFO. TheRSRreceivesserialdatafromRXterminal. Thedataisconvertedtoparallel
data and moved to the RHR. The receiver section is controlled by the line control register. If the FIFO isdisabled,
locationzerooftheFIFOisusedtostorethecharacters. (Note:Inthiscasecharactersareoverwrittenifoverflow
occurs.) If overflow occurs, characters are lost. The RHR also stores the error status bits associated with each
character.
transmit holding register (THR)
The transmitter section consists of the transmit holding register (THR) and the transmit shift register (TSR). The
transmit holding register is actually a 64-byte FIFO. The THR receives data and shifts it into the TSR where it
is converted to serial data and moved out on the TX terminal. If the FIFO is disabled, the FIFO is still used to
store the byte. Characters are lost if overflow occurs.
FIFO control register (FCR)
This is a write-only register which is used for enabling the FIFOs, clearing the FIFOs, setting transmitter and
receiver trigger levels, and selecting the type of DMA signalling. Table 9 shows FIFO control register bit settings.
Table 9. FIFO Control Register (FCR) Bit Settings
BIT NO.
BIT SETTINGS
0
0 = Disable the transmit and receive FIFOs
1 = Enable the transmit and receive FIFOs
1
2
0 = No change
1 = Clears the receive FIFO and resets counter logic to zero. Will return to zero after clearing FIFO.
0 = No change
1 = Clears the transmit FIFO and resets counter logic to zero. Will return to zero after clearing FIFO.
3
0 = DMA Mode 0
1 = DMA MOde 1
5:4
Sets the trigger level for the TX FIFO:
00 – 8 spaces
01 – 16 spaces
10 – 32 spaces
11 – 56 spaces
7:6
Sets the trigger level for the RX FIFO:
00 – 8 characters
01 – 16 characters
10 – 56 characters
11 – 60 characters
NOTE: FCR[5–4] can only be modified and enabled when EFR[4] is set. This is because the transmit trigger level is regarded as an enhanced
function.
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