LPC47M192 datasheet(77/228 Pages) SMSC

77 / 228 page

SMSC DS – LPC47M192

Page 77

Rev. 03/30/05

DATASHEET

7.6 INFRARED INTERFACE

The infrared interface provides a two-way wireless communications port using infrared as a transmission medium.

Two IR implementations have been provided for the second UART in this chip (logical device 5), IrDA and Amplitude

Shift Keyed IR. The IR transmission can use the standard UART2 TXD2 and RXD2 pins or optional IRTX2 and

IRRX2 pins. These can be selected through the configuration registers.

IrDA 1.0 allows serial communication at baud rates up to 115.2 kbps. Each word is sent serially beginning with a

zero value start bit. A zero is signaled by sending a single IR pulse at the beginning of the serial bit time. A one is

signaled by sending no IR pulse during the bit time. Please refer to the AC timing for the parameters of these pulses

and the IrDA waveform.

The Amplitude Shift Keyed IR allows asynchronous serial communication at baud rates up to 19.2K Baud. Each

word is sent serially beginning with a zero value start bit. A zero is signaled by sending a 500KHz waveform for the

duration of the serial bit time. A one is signaled by sending no transmission during the bit time. Please refer to the

AC timing for the parameters of the ASK-IR waveform.

If the Half Duplex option is chosen, there is a time-out when the direction of the transmission is changed. This time-

out starts at the last bit transferred during a transmission and blocks the receiver input until the timeout expires. If the

transmit buffer is loaded with more data before the time-out expires, the timer is restarted after the new byte is

transmitted. If data is loaded into the transmit buffer while a character is being received, the transmission will not

start until the time-out expires after the last receive bit has been received. If the start bit of another character is

received during this time-out, the timer is restarted after the new character is received. The IR half duplex time-out is

programmable via CRF2 in Logical Device 5. This register allows the time-out to be programmed to any value

between 0 and 10msec in 100usec increments.

The following figure shows the block diagram of the IR components in the LPC47M192:

ACE UART

IrDA SIR

Sharp ASK

COM

ACE

Registers

Output

MUX

COM

Host Interface

IR Options Register,

Bit 6

IR Transmit Pins

The following description pertains to the TXD2/IRTX and IRTX2 pins of the LPC47M192.

Following a VTR POR, the IRTX and IRTX2 pins will be output and low. They will remain low until one of the

following conditions are met:

IRTX2/GP35 Pin. This pin defaults to the IRTX2 function.

This pin will remain low following a VCC POR until IRTX2 function is selected for the pin, serial port 2 is

enabled by setting the activate bit, at which time the pin will reflect the state of the transmit output of the

IR block (if IR is enabled through the IR Option Register for Serial Port 2).

This pin will remain low following a VCC POR until the GPIO output function is selected for the pin, at

which time the pin will reflect the state of the GPIO data bit if it is configured as an output.

GP53/TXD2(IRTX) Pin. This pin defaults to the GPIO output function.

This pin will remain low following a VCC POR until the TXD2 (IRTX) function is selected for the pin AND

serial port 2 is enabled by setting the activate bit, at which time the pin will reflect the state of the IR

transmit output of the IR block (if IR is enabled through the IR Option Register for Serial Port 2).

LPC47M192 Datasheet(PDF) 77 Page - SMSC Corporation

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