Programmable Baud Rate Generator - Philips SC16C2550 Manual

Philips Semiconductors

6.8 Programmable baud rate generator

9397 750 11621
Product data
Dual UART with 16 bytes of transmit and receive FIFOs and IrDA
receive holding register (RHR) is read. The actual time-out value is 4 character time,
including data information length, start bit, parity bit, and the size of stop bit, i.e., 1×,
1.5×, or 2× bit times.
The SC16C2550 supports high speed modem technologies that have increased input
data rates by employing data compression schemes. For example, a 33.6 kbit/s
modem that employs data compression may require a 115.2 kbit/s input data rate.
A 128.0 kbit/s ISDN modem that supports data compression may need an input
data rate of 460.8 kbit/s. The SC16C2550 can support a standard data rate of
921.6 kbit/s.
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 frequency of up to 80 MHz. To obtain maximum data rate,
it is necessary to use full rail swing on the clock input. The SC16C2550 can be
configured for internal or external clock operation. For internal clock oscillator
operation, an industry standard microprocessor crystal is connected externally
between the XTAL1 and XTAL2 pins. Alternatively, an external clock can be
connected to the XTAL1 pin to clock the internal baud rate generator for standard or
custom rates (see Table
The generator divides the input 16× clock by any divisor from 1 to 2
SC16C2550 divides the basic external clock by 16. The basic 16× clock provides
table rates to support standard and custom applications using the same system
design. 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.
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 6 shows the selectable baud rate table available when using a 1.8432 MHz
external clock input.
1.8432 MHz
C1
47 pF
Fig 5. Crystal oscillator connection.
Rev. 03 — 19 June 2003
6).
X1
C2
100 pF
SC16C2550
encoder/decoder
− 1. The
16
1.5 kΩ
X1
1.8432 MHz
C1 C2
22 pF 47 pF
002aaa169
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
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