3

Bandwidth Selection Timing

The transceiver is in default SIR/

MIR mode when powered on.

User needs to apply the following

programming sequence to both

the SD and TXD inputs to enable

the transceiver to operate at FIR

mode.

Setting the transceiver to SIR/MIR

Mode (9.6 kbit/s to 1.152 Mbit/s)

1. Set SD/Mode input to logic

HIGH

2. TXD input should remain at

logic LOW

3. After waiting for t

SD/Mode to logic LOW, the

HIGH to LOW negative edge

transition will determine the

receiver bandwidth

4. Ensure that TXD input re-

mains low for t

receiver is now in SIR/MIR

mode

5. SD input pulse width for mode

selection should be > 50 ns.

Setting the transceiver to FIR

(4.0 Mbit/s) Mode

1. Set SD/Mode input to logic

HIGH

50%

50%

50%

TXD

SD/MODE

50%

50%

50%

TXD

SD/MODE

Figure 3. Bandwidth selection timing at SIR/MIR mode.

Figure 4. Bandwidth selection timing at FIR mode.

Transceiver I/O Truth Table

Inputs

Outputs

TXD

Light Input to Receiver

SD

LED

RXD

Note

High

Don’t Care

Low

On

Not Valid

Low

High

Low

Off

Low

12,13

Low

Low

Low

Off

High

Don’t Care

Don’t Care

High

Off

High

Notes:

12. In-band IrDA signals and data rates

≤ 4.0 Mbit/s

13. RXD logic low is a pulsed response. The condition is maintained for a duration dependent on pattern and strength of the incident intensity.

2. After SD/Mode input remains

HIGH at > 25 ns, set TXD input

to logic HIGH, wait t

(from 50% of TXD rising edge

till 50% of SD falling edge)

3. Then set SD/Mode to logic

LOW, the HIGH to LOW

negative edge transition will

determine the receiver band-

width

4. After waiting for t

set the TXD input to logic LOW

5. SD input pulse width mode

selection should be > 50 ns.