ST16C450 Exar Corporation, ST16C450 Datasheet - Page 9

• Manufacturer Part Number: ST16C450
• Description: UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER (UART)
• Manufacturer: Exar Corporation

Programmable Baud Rate Generator
The ST16C450 supports high speed modem tech-
nologies that have increased input data rates by
employing data compression schemes. For example
a 33.6Kbps modem that employs data compression
may require a 115.2Kbps input data rate. A 128.0Kbps
ISDN modem that supports data compression may
need an input data rate of 460.8Kbps. The ST16C450
can support a standard data rate of 921.6Kbps.
The programmable Baud Rate Generator is capable of
accepting an input clock up to 24 MHz, as required for
supporting a 1.5Mbps data rate. The ST16C450 can be
configured for internal or external clock operation. For
internal clock oscillator operation, an industry standard
microprocessor crystal (parallel resonant/ 22-33 pF
load) is connected externally between the XTAL1 and
XTAL2 pins, with an external 1 M resistor across it.
Baud Rate
Rev. 4.20
Table 3, BAUD RATE GENERATOR PROGRAMMING TABLE (1.8432 MHz CLOCK):
Output
115.2k
19.2k
38.4k
57.6k
1200
2400
4800
7200
9600
150
300
600
50
75
16 x Clock
(Decimal)
Divisor
User
2304
1536
768
384
192
96
48
24
16
12
6
3
2
1
16 x Clock
Divisor
(HEX)
User
900
600
300
180
C0
0C
60
30
18
10
06
03
02
01
Program
(HEX)
Value
DLM
09
06
03
01
00
00
00
00
00
00
00
00
00
00
9
Alternatively, an external clock can be connected to the
XTAL1 pin to clock the internal baud rate generator for
standard or custom rates. See figure 3 for crystal
oscillator connection.
The generator divides the input 16X clock by any
divisor from 1 to 2
basic crystal or external clock by 16. The frequency of
the -BAUDOUT output pin is exactly 16X (16 times) of
the selected baud rate (-BAUDOUT =16 x Baud Rate).
Customized Baud Rates can be achieved by selecting
the proper divisor values for the MSB and LSB sections
of baud rate generator.
Programming the Baud Rate Generator Registers DLM
(MSB) and DLL (LSB) provides a user capability for
selecting the desired final baud rate. The example in
Table 3 below.
Program
(HEX)
Value
DLL
C0
0C
00
00
00
80
60
30
18
10
06
03
02
01
16
-1. The ST16C450 divides the
ST16C450