ST16C550CQ48 EXAR [Exar Corporation], ST16C550CQ48 Datasheet - Page 10

• Manufacturer Part Number: ST16C550CQ48
• Manufacturer: EXAR [Exar Corporation]

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.
Rev. 4.30
Table 3, BAUD RATE GENERATOR PROGRAMMING TABLE (1.8432 MHz CLOCK):
Divisor (in decimal) = (XTAL1 clock frequency) / (serial data rate x 16)
Baud Rate
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
01
60
30
18
10
06
03
02
10
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 M 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 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 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:
Program
Value
(HEX)
DLM
09
06
03
01
00
00
00
00
00
00
00
00
00
00
Program
Value
(HEX)
16
DLL
C0
0C
00
00
00
80
60
30
18
10
06
03
02
01
-1. The ST16C550 divides the