
(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.
Figure 2 shows the block diagram of the IR components in the LPC47S42x:
89
ACE UART
IrDA SIR
Sharp ASK
COM
ACE
Registers
Output
MUX
IR
COM
Host Interface
IR Options Register,
Bit 6
FIGURE 2
IR Transmit Pin
The following description pertains to the IRTX pin of the LPC47S42x.
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.