XR16L2552
2.25V TO 5.5V DUART WITH 16-BYTE FIFO
xr
REV. 1.1.1
12
2.12
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 16 bytes of FIFO which
includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X internal
clock. A bit time is 16 clock periods. The transmitter sends the start-bit followed by the number of data bits,
inserts the proper parity-bit if enabled, and adds the stop-bit(s). The status of the FIFO and TSR are reported in
the Line Status Register (LSR bit-5 and bit-6).
2.12.1
Transmit Holding Register (THR) - Write Only
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.
2.12.2
Transmitter Operation in non-FIFO Mode
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.
Transmitter
2.12.3
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
transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when the FIFO and the TSR
become empty.
Transmitter Operation in FIFO Mode
153.6k
6
06
00
06
0
230.4k
4
04
00
04
0
460.8k
2
02
00
02
0
921.6k
1
01
00
01
0
F
IGURE
7. T
RANSMITTER
O
PERATION
IN
NON
-FIFO M
ODE
T
ABLE
5: T
YPICAL
DATA
RATES
WITH
A
14.7456 MH
Z
CRYSTAL
OR
EXTERNAL
CLOCK
O
UTPUT
Data Rate
MCR Bit-7=0
D
IVISOR
FOR
16x
Clock (Decimal)
D
IVISOR
FOR
16x
Clock (HEX)
DLM P
ROGRAM
V
ALUE
(HEX)
DLL P
ROGRAM
V
ALUE
(HEX)
D
ATA
R
ATE
E
RROR
(%)
Transmit
Holding
Register
(THR)
Transmit Shift Register (TSR)
Data
Byte
L
S
B
M
S
B
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
TXNOFIFO1
16X
Clock