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2016-04-28 - Giant Gecko Family - d0053_Rev1.20
473
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The transmission interrupt vector groups the transmission-related interrupts generated by the following
interrupt flags:
• TXC
• TXBL
• TXOF
• CCF
The reception interrupt on the other hand groups the reception-related interrupts, triggered by the
following interrupt flags:
• RXDATAV
• RXFULL
• RXOF
• RXUF
• PERR
• FERR
• MPAF
• SSM
If USART interrupts are enabled, an interrupt will be made if one or more of the interrupt flags in
USART_IF and their corresponding bits in USART_IEN are set.
17.3.9 IrDA Modulator/Demodulator
The IrDA modulator onUSART0 implements the physical layer of the IrDA specification, which is
necessary for communication over IrDA. The modulator takes the signal output from the USART module,
and modulates it before it leaves USART0 . In the same way, the input signal is demodulated before
it enters the actual USART module. The modulator is only available on USART0 , and implements the
original Rev. 1.0 physical layer and one high speed extension which supports speeds from 2.4 kbps
to 1.152 Mbps.
The data from and to the USART is represented in a NRZ (Non Return to Zero) format, where the signal
value is at the same level through the entire bit period. For IrDA, the required format is RZI (Return to
Zero Inverted), a format where a “1” is signalled by holding the line low, and a “0” is signalled by a short
high pulse. An example is given in Figure 17.21 (p. 473) .
Figure 17.21. USART Example RZI Signal for a given Asynchronous USART Frame
S
0
1
2
3
4
5
6
7
P
St op
Idle
Idle
USART
(NRZ)
IrDA
(RZI)
The IrDA module is enabled by setting IREN. The USART transmitter output and receiver input is then
routed through the IrDA modulator.
The width of the pulses generated by the IrDA modulator is set by configuring IRPW in
USARTn_IRCTRL. Four pulse widths are available, each defined relative to the configured bit period
as listed in Table 17.10 (p. 474) .
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