XR16L570 Exar Corporation, XR16L570 Datasheet - Page 11

• Manufacturer Part Number: XR16L570
• Description: SMALLEST 1.62V TO 5.5V UART
• Manufacturer: Exar Corporation

xr
REV. 1.0.0
F
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
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The Transmitter Empty Flag (LSR bit-6) is set when both the TSR and the FIFO become empty.
The receiver section contains an 8-bit Receive Shift Register (RSR) and 16 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X clock for timing. On the falling edge of a
start or a false start bit, an internal receiver counter starts counting at the 16X clock rate. After 8 clocks the start
bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic 0 it is
validated as a start bit. Evaluating the start bit in this manner prevents the receiver from assembling a false
character. Each of the data, parity and stop bits is sampled at the middle of the bit to prevent false framing. If
there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte
from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status
of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character
or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a
receive data ready time-out interrupt when data is not received for 4 word lengths as defined by LCR[1:0] plus
12 bits time. This is equivalent to 3.7-4.6 character times. The RHR interrupt is enabled by IER bit-0.
F
2.11
2.10.3
IGURE
IGURE
7. T
8. T
RECEIVER
Transmitter Operation in FIFO Mode
RANSMITTER
RANSMITTER
Auto CTS Flow Control (CTS# pin)
Auto Software Flow Control
(Xoff1,2 and Xon1,2 Reg.)
Flow Control Characters
16X Clock
O
O
16X Clock
PERATION IN NON
PERATION IN
Data
Byte
SMALLEST 1.62V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE
Data Byte
Transmit
Transmit Shift Register (TSR)
FIFO
-FIFO M
Transmit
Register
Holding
(THR)
AND
Transm it Data Shift Register
F
LOW
ODE
Transm it
FIFO
(TSR)
11
C
ONTROL
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
FIFO is Enabled by FCR bit-0=1
THR Interrupt (ISR bit-1):
M
- W hen the TX FIFO falls below the
- W hen the TX FIFO becomes em pty.
ODE
programmed Trigger Level, and
M
S
B
TXNOFIFO1
L
S
B
T XF IF O 1
XR16L570