xr16m554 Exar Corporation, xr16m554 Datasheet - Page 15

• Manufacturer Part Number: xr16m554
• Description: 1.62v To 3.63v Quad Uart With 16-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.0
The transmit holding register is an 8-bit register providing a data interface to the host processor. The host
writes transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits,
parity-bit and stop-bit(s). The least-significant-bit (Bit-0) becomes first data bit to go out. The THR is the input
register to the transmit FIFO of 16 bytes when FIFO operation is enabled by FCR bit-0. Every time a write
operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data
location.
The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the
data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled
by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.
The host may fill the transmit FIFO with up to 16 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
FIFO becomes empty. The transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set
when TSR/FIFO becomes empty.
F
F
2.9.1
2.9.2
2.9.3
IGURE
IGURE
7. T
8. T
Transmit Holding Register (THR) - Write Only
Transmitter Operation in non-FIFO Mode
Transmitter Operation in FIFO Mode
RANSMITTER
RANSMITTER
16X Clock
O
O
16X Clock
PERATION IN NON
PERATION IN
Data Byte
Transmit
Data
Byte
Transmit Shift Register (TSR)
FIFO
Transmit Data Shift Register
-FIFO M
AND
Transmit
Register
Holding
(THR)
Transmit
( TSR )
FIFO
F
LOW
ODE
15
C
1.62V TO 3.63V QUAD UART WITH 16-BYTE FIFO
ONTROL
THR Interrupt (ISR bit-1)
When it becomes empty.
Bit-0=1
THR Interrupt (ISR bit-1)
M
FIFO is Enabled by FCR
Enabled by IER bit-1
ODE
M
S
B
L
S
B
TXNOFIFO1
TXFIFO1
XR16M554/554D