SC16C650B Datasheet, PDF (12/48 Pages) NXP Semiconductors – 5 V, 3.3 V and 2.5 V UART with 32-byte FIFOs and infrared (IrDA) encoder/decoder

NXP Semiconductors
SC16C650B
UART with 32-byte FIFOs and IrDA encoder/decoder
6.7 Programmable baud rate generator
The SC16C650B 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.
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
accepting an input clock up to 48 MHz, as required for supporting a 3 Mbit/s data rate.
The SC16C650B can be configured for internal or external clock operation. For internal
clock oscillator operation, an industry standard microprocessor crystal (parallel resonant,
22 pF to 33 pF load) is connected externally between the XTAL1 and XTAL2 pins (see
Figure 5). 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 5).
XTAL1
XTAL2
X1
1.8432 MHz
XTAL1
XTAL2
1.5 kΩ
X1
1.8432 MHz
C1
22 pF
C2
33 pF
C1
22 pF
C2
47 pF
002aaa870
Fig 5. Crystal oscillator connection
The generator divides the input 16× clock by any divisor from 1 to (2¹⁶ − 1). The
SC16C650B divides the basic crystal or external clock by 16. The frequency of the
BAUDOUT output pin is exactly 16× (16 times) the selected baud rate
(BAUDOUT = 16 × baud rate). Customized baud rates can be achieved by selecting the
proper divisor values for the MSB and LSB sections of baud rate generator.
Setting MCR[7] to a logic 1 provides an additional divide-by-4, whereas setting MCR[7] to
a logic 0 only divides by 1 (see Table 5 and Figure 6).
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 5 shows
selectable baud rates when using a 1.8432 MHz crystal and setting MCR[7] to a logic 0.
For custom baud rates, the divisor value can be calculated using Equation 1:
divisor (in decimal) = -^X----^Ts---_eA---_r-^L--_i--_a1---_l--^c--_d-^l--^oa----^ct--_a-^k----_r-^f--_a-^r--_te--_e-^q---_×-^u---^e-₁--ⁿ-₆--^c---^y--
(1)
SC16C650B_4
Product data sheet
Rev. 04 — 14 September 2009
© NXP B.V. 2009. All rights reserved.
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