ST16C550(2003) 데이터 시트보기 (PDF) - Exar Corporation
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ST16C550 Datasheet PDF : 35 Pages
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ST16C550
T = [(programmed word length = 7) + (stop bit = 1) +
(start bit = 1) = 9]. 40 (bit times divided by 9) = 4.4
characters.
Example -B: If the user programs the word length = 7,
with parity and one stop bit, the time out will be:
T = 4 X 7(programmed word length) + 12 = 40 bit times.
Character time = 40 / 10 [ (programmed word length
= 7) + (parity = 1) + (stop bit = 1) + (start bit = 1) = 4
characters.
Programmable Baud Rate Generator
The ST16C550 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 ST16C550
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 ST16C550 can
be configured for internal or external clock operation.
For internal clock oscillator operation, an industry
standard microprocessor crystal (parallel resonant/ 22
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 ST16C550 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 sec-
tions 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 shows selectable baud rates when
using a 1.8432 MHz crystal.
For custom baud rates, the divisor value can be calcu-
lated using the following equation:
Divisor (in decimal) = (XTAL1 clock frequency) / (serial data rate x 16)
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)
DLL
Program
Value
(HEX)
50
2304
900
09
00
75
1536
600
06
00
150
768
300
03
00
300
384
180
01
80
600
192
C0
00
C0
1200
96
60
00
60
2400
48
30
00
30
4800
24
18
00
18
7200
16
10
00
10
9600
12
0C
00
0C
19.2k
6
06
00
06
38.4k
3
03
00
03
57.6k
2
02
00
02
115.2k
1
01
00
01
Rev. 4.30
10
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