June 1995
PC16550D Universal Asynchronous
²
Receiver/Transmitter with FIFOs
General Description
Features
Y
Capable of running all existing 16450 software.
Pin for pin compatible with the existing 16450 except
for CSOUT (24) and NC (29). The former CSOUT and
NC pins are TXRDY and RXRDY, respectively.
After reset, all registers are identical to the 16450 reg-
ister set.
The PC16550D is an improved version of the original 16450
Universal Asynchronous Receiver/Transmitter (UART).
Functionally identical to the 16450 on powerup (CHARAC-
TER mode)* the PC16550D can be put into an alternate
mode (FIFO mode) to relieve the CPU of excessive software
overhead.
Y
Y
Y
In this mode internal FIFOs are activated allowing 16 bytes
(plus 3 bits of error data per byte in the RCVR FIFO) to be
stored in both receive and transmit modes. All the logic is on
chip to minimize system overhead and maximize system ef-
ficiency. Two pin functions have been changed to allow sig-
nalling of DMA transfers.
In the FIFO mode transmitter and receiver are each
buffered with 16 byte FIFO’s to reduce the number of
interrrupts presented to the CPU.
Y
Y
Adds or deletes standard asynchronous communication
bits (start, stop, and parity) to or from the serial data.
Holding and shift registers in the 16450 Mode eliminate
the need for precise synchronization between the CPU
and serial data.
The UART performs serial-to-parallel conversion on data
characters received from a peripheral device or a MODEM,
and parallel-to-serial conversion on data characters re-
ceived from the CPU. The CPU can read the complete
status of the UART at any time during the functional opera-
tion. Status information reported includes the type and con-
dition of the transfer operations being performed by the
UART, as well as any error conditions (parity, overrun, fram-
ing, or break interrupt).
Y
Y
Independently controlled transmit, receive, line status,
and data set interrupts.
Programmable baud generator divides any input clock
16
b
Independent receiver clock input.
c
clock.
by 1 to (2
1) and generates the 16
Y
Y
MODEM control functions (CTS, RTS, DSR, DTR, RI,
and DCD).
The UART includes a programmable baud rate generator
that is capable of dividing the timing reference clock input
16
Y
Fully programmable serial-interface characteristics:
Ð 5-, 6-, 7-, or 8-bit characters
Ð Even, odd, or no-parity bit generation and detection
Ð 1-, 1(/2-, or 2-stop bit generation
Ð Baud generation (DC to 1.5M baud).
False start bit detection.
b
c
clock for
driving the internal transmitter logic. Provisions are also in-
by divisors of 1 to (2
1), and producing a 16
c
cluded to use this 16 clock to drive the receiver logic. The
UART has complete MODEM-control capability, and a proc-
essor-interrupt system. Interrupts can be programmed to
the user’s requirements, minimizing the computing required
to handle the communications link.
Y
Y
Y
Y
Y
Complete status reporting capabilities.
TRI-STATE TTL drive for the data and control buses.
É
Line break generation and detection.
The UART is fabricated using National Semiconductor’s ad-
2
vanced M CMOS process.
Internal diagnostic capabilities:
Ð Loopback controls for communications link fault
isolation
*Can also be reset to 16450 Mode under software control.
Ð Break, parity, overrun, framing error simulation.
Full prioritized interrupt system controls.
²
Note: This part is patented.
Y
Basic Configuration
TL/C/8652–1
TRI-STATEÉ is a registered trademark of National Semiconductor Corp.
C
1995 National Semiconductor Corporation
TL/C/8652
RRD-B30M75/Printed in U. S. A.