16C450 Просмотр технического описания (PDF) - Exar Corporation
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16C450 Datasheet PDF : 28 Pages
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ST16C450
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 MΩ resistor across it.
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 216 -1. The ST16C450 divides the
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.
Table 3, BAUD RATE GENERATOR PROGRAMMING TABLE (1.8432 MHz CLOCK):
Output
Baud Rate
User
16 x Clock
Divisor
(Decimal)
User
16 x Clock
Divisor
(HEX)
DLM
Program
Value
(HEX)
50
2304
900
09
75
1536
600
06
150
768
300
03
300
384
180
01
600
192
C0
00
1200
96
60
00
2400
48
30
00
4800
24
18
00
7200
16
10
00
9600
12
0C
00
19.2k
6
06
00
38.4k
3
03
00
57.6k
2
02
00
115.2k
1
01
00
DLL
Program
Value
(HEX)
00
00
00
80
C0
60
30
18
10
0C
06
03
02
01
Rev. 4.20
9
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