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UART / RS-232 Notes for EEL4744 Summer 2008 Course at University of Florida - Prof. Karl S, Study notes of Microprocessors

University of Florida (UF)Microprocessors
Prof. Karl S. Gugel

Detailed information about the tl16c550 asynchronous communications ic used for full duplex rs-232 communication. It includes pin definitions, suggested wiring diagram, and steps to initialize the uart. It is a part of the electrical and computer engineering course eel4744 taught by drs. Schwartz and gugel during summer 2008.

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Uploaded on 03/10/2009

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University of Florida EEL4744 – Summer 2008 Drs. E. M. Schwartz and K. Gugel
Electrical and Computer Engineering John A. Martiney, former TA
Page 1/4 Revision 0 16-Jun-08
UART / RS-232 Notes
Brief Device Description
The TL16C550 is an Asynchronous Communications IC that supports one channel of full duplex
RS232 communication. It features double buffering of both transmit and receive characters. It
also offers programmable data lengths (5-8 bits), even/odd/no parity, 1/2 bit stop bit generation
and a wide variety of programmable baud rates. See the datasheet available at Texas Instrument's
web site (www.ti.com) for more information and the data sheet from TI at
http://www-s.ti.com/sc/ds/tl16c550c.pdf (also available on our website).
Pin Definitions
See the suggested wiring diagram on the following page.
Pin Name Description
A2:0 Address line inputs for selecting internal registers
~ADS Address strobe input that can be used to internally latch a dynamic address
bus value. Note: If your µP supports static address, this input can be simply
grounded.
D7:0 Bi-directional TTL level data bus used to R/W from internal registers.
~BAUDOUT Output that is system clock divided by 16 and then divided by BAUD
register contents.
CS0, CS1, ~CS2 Chip select inputs, where all must be true to allow reads/writes to internal
registers.
~TXREADY,
~RXREADY Transmitter/Receive DMA signaling ready.
~CTS, ~DCD,
~DSR, ~DTR,
~RI, ~RTS,
~OUT1, ~OUT2
Modem communication pins not required in basic RS232 communication.
DDIS Output, that is high when the UART is not being read. Can be used to control
external transceiver.
RD2, ~RD1 Data input strobes used to read data from the UART. Attach one to the read
signal of your uP and then always DISABLE the other.
WR2, ~WR1 Data output strobes used to write data to the UART. Attach one to the ~write
signal of uP and then always DISABLE the other.
INTRPT Interrupt pin (high true) that can be used to initiate an interrupt on the uP.
MR Master reset input that resets the UART when high.
RCLK Receiver clock input that is tied to -BAUDOUT in most cases.
SIN Serial input (RX line)
SOUT Serial output (TX line)
Vcc, Vss +5V, Ground
XIN, XOUT System clock or crystal inputs.
pf3
pf4

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Download UART / RS-232 Notes for EEL4744 Summer 2008 Course at University of Florida - Prof. Karl S and more Study notes Microprocessors in PDF only on Docsity!

Electrical and Computer Engineering John A. Martiney, former TA Page 1/4 Revision 0 16-Jun- UART / RS-232 Notes

Brief Device Description

The TL16C550 is an Asynchronous Communications IC that supports one channel of full duplex RS232 communication. It features double buffering of both transmit and receive characters. It also offers programmable data lengths (5-8 bits), even/odd/no parity, 1/2 bit stop bit generation and a wide variety of programmable baud rates. See the datasheet available at Texas Instrument's web site (www.ti.com) for more information and the data sheet from TI at http://www-s.ti.com/sc/ds/tl16c550c.pdf (also available on our website).

Pin Definitions

See the suggested wiring diagram on the following page. Pin Name Description

A2:0 Address line inputs for selecting internal registers ~ADS Address strobe input that can be used to internally latch a dynamic address bus value. Note: If your μP supports static address, this input can be simply grounded. D7:0 Bi-directional TTL level data bus used to R/W from internal registers. ~BAUDOUT Output that is system clock divided by 16 and then divided by BAUD register contents. CS0, CS1, ~CS2 Chip select inputs, where all must be true to allow reads/writes to internal registers. ~TXREADY, ~RXREADY

Transmitter/Receive DMA signaling ready.

~CTS, ~DCD, ~DSR, ~DTR, ~RI, ~RTS, ~OUT1, ~OUT

Modem communication pins not required in basic RS232 communication.

DDIS Output, that is high when the UART is not being read. Can be used to control external transceiver. RD2, ~RD1 Data input strobes used to read data from the UART. Attach one to the read signal of your uP and then always DISABLE the other. WR2, ~WR1 Data output strobes used to write data to the UART. Attach one to the ~write signal of uP and then always DISABLE the other. INTRPT Interrupt pin (high true) that can be used to initiate an interrupt on the uP. MR Master reset input that resets the UART when high. RCLK Receiver clock input that is tied to -BAUDOUT in most cases. SIN Serial input (RX line) SOUT Serial output (TX line) Vcc, Vss +5V, Ground XIN, XOUT System clock or crystal inputs.

Electrical and Computer Engineering John A. Martiney, former TA Page 2/4 Revision 0 16-Jun- UART / RS-232 Notes

Suggested Elementary Microprocessor Interface Wiring

Notes:

  1. See the UART spec sheet for pinout of this device.
  2. Connect a 0.1 μF capacitor between power and ground pins (not shown above). (VCC is pin 40 and GND (VSS) is pin 20.)
  3. All other pins not shown above are left open (i.e., no connection).
  4. ~UART_CE is a decoded signal in the microprocessor's memory map. You will generate this signal using your CPLD.
  5. ~Reset is the microcontroller system’s active-low reset.
  6. All inverters shown in the schematic can be placed in the CPLD used for address decoding.

D7-D

INTRPT MR A A A ~ADS WR ~WR RD ~RD ~CS2 CS1 CS

~BAUDOUT RCLK

XIN

SIN

SOUT

uP D7-D

uP ~IRQ ~RESET uP A uP A uP A GND GND

VCC

TL16C

uP R/~W uP R/~W

CLK Out (From 1. MHz Clock)

VCC VCC

~UART_CE

R1OUT (From RS-232)

T1IN (To RS-232)

1.8432 MHz Clock

+5V

no connect

CLK Out

GND

TOP VIEW

Electrical and Computer Engineering John A. Martiney, former TA Page 4/4 Revision 0 16-Jun- UART / RS-232 Notes

Data Length & Stop Bit Initialization

  1. Set D1 & D0 to the appropriate values in the Line Control Register (LCR). Note: For data word lengths = 8 bits, D1 and D0 in LCR are both set high. See data page 28 for additional word length bit field definitions if necessary.
  2. Set D2 in the LCR low if only one stop bit is desired, else set high if 2 stop bits are desired.

Enabling a TX or RX Interrupt

  1. Set D0 high in the Interrupt Enable Register (IER) if you desire to generate an interrupt when new characters are received.
  2. Set D1 high in the IER if you desire to generate an interrupt when the transmit buffer is empty.

Suggested Early Functional Testing

  1. Verify that you can write and read to registers in the UART without error.
  2. Try sending out characters by polling the Transmitter Holding Register (THRE) bit and Transmitter Empty (TEMT) bit in the Line Status Register (LSR). If THRE is high, you can write a new character to the transmit buffer.
  3. Try reading in a character by sending characters from hyper terminal and writing code to poll the Data Ready (DR) bit in the Line Status Register (LSR). If Data Ready is high, a character can be read from the receive buffer.
  4. Once polling works, move on to generating an interrupt with the UART when a character has been received. Your ISR should read the Interrupt Identification Register (IIR) and check bits D3:0. You should see '0100' on these bits indicating a character has been received. Read the character and transmit using polling.
  5. Enable both RX and TX interrupts in the UART. Modify your interrupt handler to read/test D3:0 in the IIR such that if 0'100' is detected jump to code to read the character in and if '0010' is detected then write a character out. See "Table 5. Interrupt Control Functions" in the 16C550 data sheet for more details on these bit field definitions.