6.6 Infrared Interface
The infrared interface provides a two-way wireless communications port using infrared as a transmission medium.
Several 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. 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 LPC47S45x:
ACE
Registers
COM
IR
Output
MUX
Host Interface
IrDA SIR
Sharp ASK
COM
ACE UART
IR Options Register,
Bit 6
6.6.1 IR TRANSMIT PIN
The following description pertains to the IRTX pin of the LPC47S45x.
Following a VTR POR, the IRTX pin will be output and low. It will remain low until one of the following conditions are
met:
GP53/TXD2/IRTX Pin. This pin defaults to the GPIO function.
1. This pin will remain low following a VCC POR until the 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 IRCC
block (if IR is enabled through the IR Option Register for Serial Port 2).
2. This pin will remain low following a VCC POR until the TXD2 function is selected for the pin AND serial port 2 is
enabled by setting the activate bit, at which the pin will reflect the state of the transmit output of serial port 2 (if
COM is enabled through the IR Option Register for Serial Port 2).
3. This pin will remain low following a VCC POR until the corresponding GPIO data bit (GP5 register bit 3) is set or
the polarity bit in the GP53 control register is set.
SMSC DS – LPC47S45x
Page 76 of 259
Rev. 07/09/2001
DATASHEET
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