SC16C550 Datasheet, PDF (17/52 Pages) NXP Semiconductors – Universal Asynchronous Receiver/Transmitter (UART) with 16-byte FIFO and infrared (IrDA) encoder/decoder

Philips Semiconductors
SC16C550
UART with 16-byte FIFO and IrDA encoder/decoder
6.9 Sleep mode
The SC16C550 is designed to operate with low power consumption. A special sleep
mode is included to further reduce power consumption when the chip is not being
used. With EFR[4] and IER[4] enabled (set to a logic 1), the SC16C550 enters the
sleep mode, but resumes normal operation when a start bit is detected, a change of
state on any of the modem input pins RX, RI, CTS, DSR, DCD, or a transmit data is
provided by the user. If the sleep mode is enabled and the SC16C550 is awakened by
one of the conditions described above, it will return to the sleep mode automatically
after the last character is transmitted or read by the user. In any case, the sleep mode
will not be entered while an interrupt(s) is pending. The SC16C550 will stay in the
sleep mode of operation until it is disabled by setting IER[4] to a logic 0.
6.10 Loop-back mode
The internal loop-back capability allows on-board diagnostics. In the loop-back mode,
the normal modem interface pins are disconnected and reconfigured for loop-back
internally. MCR[0-3] register bits are used for controlling loop-back diagnostic testing.
In the loop-back mode, OUT1 and OUT2 in the MCR register (bits 3-2) control the
modem RI and DCD inputs, respectively. MCR signals DTR and RTS (bits 0-1) are
used to control the modem CTS and DSR inputs, respectively. The transmitter output
(TX) and the receiver input (RX) are disconnected from their associated interface
pins, and instead are connected together internally (see Figure 10). The CTS, DSR,
DCD, and RI are disconnected from their normal modem control input pins, and
instead are connected internally to DTR, RTS, OUT1 and OUT2. Loop-back test data
is entered into the transmit holding register via the user data bus interface, D0-D7.
The transmit UART serializes the data and passes the serial data to the receive
UART via the internal loop-back connection. The receive UART converts the serial
data back into parallel data that is then made available at the user data interface
D0-D7. The user optionally compares the received data to the initial transmitted data
for verifying error-free operation of the UART TX/RX circuits.
In this mode, the receiver and transmitter interrupts are fully operational. The Modem
Control Interrupts are also operational. However, the interrupts can only be read
using lower four bits of the Modem Status Register (MSR[0-3]) instead of the four
Modem Status Register bits 4-7. The interrupts are still controlled by the IER.
9397 750 11619
Product data
Rev. 05 — 19 June 2003
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
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