XR17L154 Datasheet, PDF (29/56 Pages) Exar Corporation – 3.3V PCI BUS QUAD UART

XR17L154
3.3V PCI BUS QUAD UART
REV. 1.1.0
áç
DISCONTINUED
TABLE 11: UART CHANNEL CONFIGURATION REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED BY EFR BIT-4.
ADDRESS
A3-A0
REG
NAME
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0 COMMENT
1 1 0 0 XCHAR R
0
0
0
0
0
0
Xon Det. Xoff Det. Self-clear
Indicator Indicator after read
1 1 0 0 XOFF1 W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 1 0 1 XOFF2 W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 1 1 0 XON1
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
1 1 1 1 XON2
W
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
NOTE: MCR bits 2 and 3 (OP1 and OP2 outputs) are not available in the XR17L154. They are present for 16C550
compatibility during Internal loopback, see Figure 11.
4.6 Transmitter
The transmitter section comprises of a 64 bytes of FIFO, a byte-wide Transmit Holding Register (THR) and an
8-bit Transmit Shift Register (TSR). THR receives a data byte from the host (non-FIFO mode) or a data byte
from the FIFO when the FIFO is enabled by FCR bit-0. TSR shifts out every data bit with the 16X or 8X internal
clock. A bit time is 16 or 8 clock periods. The transmitter sends the start bit followed by the number of data bits,
inserts the proper parity bit if enable, and adds the stop bit(s). The status of the THR and TSR are reported in
the Line Status Register (LSR bit-5 and bit-6).
4.6.1 Transmit Holding Register (THR)
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 also the
input register to the transmit FIFO of 64 bytes when FIFO operation is enabled by FCR bit-0. A THR empty
interrupt can be generated when it is enabled in IER bit-1.
4.6.2 Transmitter Operation in non-FIFO
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.
FIGURE 12. TRANSMITTER OPERATION IN NON-FIFO MODE
D a ta
B y te
16X or 8X
C lock
(8XM ODE
R egister)
Transm it
H olding
R egister
(T H R )
TH R Interrupt (ISR bit-1)
Enabled by IER bit-1
Transm it Shift R egister (TSR)
M
L
S
S
B
B
T X N O F IF O 1
29