PC16550D Datasheet, PDF (1/22 Pages) National Semiconductor (TI) – PC16550D Universal Asynchronous Receiver/Transmitter with FIFOs

June 1995
PC16550D Universal Asynchronous
Receiver Transmitter with FIFOs
General Description
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
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
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)
The UART includes a programmable baud rate generator
that is capable of dividing the timing reference clock input
by divisors of 1 to (2¹⁶b1) and producing a 16 c clock for
driving the internal transmitter logic Provisions are also in-
cluded to use this 16 c 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
The UART is fabricated using National Semiconductor’s ad-
vanced M²CMOS process
Can also be reset to 16450 Mode under software control
Note This part is patented
Features
Y _{Capable of running all existing 16450 software}
Y _{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
Y _{After reset all registers are identical to the 16450 reg-}
ister set
Y _{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 _{Adds or deletes standard asynchronous communication}
bits (start stop and parity) to or from the serial data
Y _{Holding and shift registers in the 16450 Mode eliminate}
the need for precise synchronization between the CPU
and serial data
Y _{Independently controlled transmit receive line status}
and data set interrupts
Y _{Programmable baud generator divides any input clock}
by 1 to (2¹⁶ b 1) and generates the 16 c clock
Y _{Independent receiver clock input}
Y _{MODEM control functions (CTS RTS DSR DTR RI}
and DCD)
Y _{Fully programmable serial-interface characteristics}
5- 6- 7- or 8-bit characters
Even odd or no-parity bit generation and detection
1- 1 - or 2-stop bit generation
Baud generation (DC to 1 5M baud)
Y _{False start bit detection}
Y _{Complete status reporting capabilities}
Y _{TRI-STATE TTL drive for the data and control buses}
Y _{Line break generation and detection}
Y _{Internal diagnostic capabilities}
Loopback controls for communications link fault
isolation
Break parity overrun framing error simulation
Y _{Full prioritized interrupt system controls}
Basic Configuration
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