xr
XR16C2852
REV. 2.1.1
2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
11
divisor between 1 and (216 -1) to obtain a 16X sampling rate clock of the serial data rate. The sampling rate
clock is used by the transmitter for data bit shifting and receiver for data sampling.
Programming the Baud Rate Generator Registers DLM and DLL provides the capability of selecting the
operating data rate.
Table 5 shows the standard data rates available with a 14.7456 MHz crystal or external
clock at 16X sampling rate clock rate. When using a non-standard data rate crystal or external clock, the
divisor value can be calculated for DLL/DLM with the following equation.
2.11
Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 128 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).
FIGURE 6. BAUD RATE GENERATOR AND PRESCALER
divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16)
TABLE 5: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK
OUTPUT Data Rate
MCR Bit-7=1
OUTPUT Data Rate
MCR Bit-7=0
(DEFAULT)
DIVISOR FOR 16x
Clock (Decimal)
DIVISOR FOR 16x
Clock (HEX)
DLM
PROGRAM
VALUE (HEX)
DLL
PROGRAM
VALUE (HEX)
DATA RATE
ERROR (%)
100
400
2304
900
09
00
0
600
2400
384
180
01
80
0
1200
4800
192
C0
00
C0
0
2400
9600
96
60
00
60
0
4800
19.2k
48
30
00
30
0
9600
38.4k
24
18
00
18
0
19.2k
76.8k
12
0C
00
0C
0
38.4k
153.6k
6
06
00
06
0
57.6k
230.4k
4
04
00
04
0
115.2k
460.8k
2
02
00
02
0
230.4k
921.6k
1
01
00
01
0
XTAL1
XTAL2
Crystal
Osc/
Buffer
MCR Bit-7=0
(default)
MCR Bit-7=1
DLL and DLM
Registers
Prescaler
Divide by 1
Prescaler
Divide by 4
16X
Sampling
Rate Clock to
Transmitter
Baud Rate
Generator
Logic