TIR1000, TIR1000I

STANDALONE IrDA

™ ENCODER AND DECODER

SLLS228F – DECEMBER 1995 – REVISED JULY 1999

3

POST OFFICE BOX 655303

switching characteristics

PARAMETER

TEST CONDITIONS

MIN

TYP†

MAX

UNIT

tr

Output rise time

C(LOAD) = 15 pF (10% to 90%)

1.3

ns

tf

Output fall time

C(LOAD)= 15 pF (90% to 10%)

1.8

ns

† Typical values are at TA = 25°C.

APPLICATION INFORMATION

To LED

From

TERMINAL

Optoelectronics

U_TXD

U_RXD

16XCLK

IR_TXD

IR_RXD

RESET

SOUT

SIN

BAUDOUT

RESET

TL16C550C UART

TIR1000, TIR1000I

Figure 1. Typical application of the TIR1000, TIR1000I

PRINCIPLES OF OPERATION

IrDA overview

The Infrared Data Association (IrDA) defines several protocols for sending and receiving serial infrared data,

including rates of 115.2 kbps, 0.576 Mbps, 1.152 Mbps, and 4 Mbps. The low rate of 115.2 kbps was specified

first and the others must maintain downward compatibility with it. At the 115.2 kbps rate, the protocol

implemented in the hardware is fairly simple. It primarily defines a serial infrared data

word to be surrounded

by a start bit equal to 0 and a stop bit equal to 1. Individual bits are encoded or decoded the same whether they

are start, data, or stop bits. The TIR1000 and TIR1000I evaluate only single bits and only follow the 115.2 kbps

protocol. The 115.2 kbps rate is a maximum rate. When both ends of the transfer are set up to a lower but

matching speed, the protocol (with the TIR1000 and TIR1000I) still works. The clock used to code or sample

the data is 16 times the baud rate, or 1.843 Mhz maximum. To code a 1, no pulse is sent or received for 1-bit

time period, or 16 clock cycles. To code a 0, one pulse is sent or received within a 1-bit time period, or 16 clock

cycles. The pulse must be at least 1.6

µs wide and 3 clock cycles long at 1.843 Mhz. At lower baud rates the

pulse can be 1.6

µs wide or as long as 3 clock cycles. The transmitter output, IR_TXD, is intended to drive a

LED circuit to generate an infrared pulse. The LED circuits work on positive pulses. A terminal circuit is expected

to create the receiver input, IR_RXD. Most, but not all, PIN circuits have inversion and generate negative pulses

from the detected infrared light. Their output is normally high. The TIR1000 and TIR1000I can decode either

negative or positive pulses on IR_RXD.