ST16C2450 Просмотр технического описания (PDF) - Exar Corporation
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ST16C2450 Datasheet PDF : 30 Pages
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ST16C2450
2.97V TO 5.5V DUART
xr
REV. 4.0.1
2.7 Programmable Baud Rate Generator
A single baud rate generator is provided for the transmitter and receiver, allowing independent TX/RX channel
control. The programmable Baud Rate Generator is capable of operating with a crystal frequency or external
clock of up to 24 MHz.
The 2450 divides the basic external clock by 16. The basic 16X clock provides table rates to support standard
and custom applications using the same system design. The Baud Rate Generator divides the input 16X clock
by any divisor from 1 to 216 -1. The rate table is configured via the DLL and DLM internal register functions.
Customized Baud Rates can be achieved by selecting the proper divisor values for the MSB and LSB sections
of baud rate generator.
Table 3 shows the standard data rates available with a 14.7456 MHz crystal or external clock at 16X sampling
rate. When using a non-standard frequency crystal or external clock, the divisor value can be calculated for
DLL/DLM with the following equation.
divisor (decimal) = (XTAL1 clock frequency) / (serial data rate x 16)
TABLE 3: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK
OUTPUT Data Rate DIVISOR FOR 16x DIVISOR FOR 16x
MCR Bit-7=0
Clock (Decimal) Clock (HEX)
400
2304
900
2400
384
180
4800
192
C0
9600
96
60
19.2k
48
30
38.4k
24
18
76.8k
12
0C
153.6k
6
06
230.4k
4
04
460.8k
2
02
921.6k
1
01
DLM PROGRAM
VALUE (HEX)
09
01
00
00
00
00
00
00
00
00
00
DLL PROGRAM
VALUE (HEX)
00
80
C0
60
30
18
0C
06
04
02
01
DATA RATE
ERROR (%)
0
0
0
0
0
0
0
0
0
0
0
2.8 Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 1 byte FIFO or 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).
2.8.1 Transmit Holding Register (THR) - Write Only
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.
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