UART/IrDA Modes of Operation
12-86
12.8.2.4
Pulse Shaping
In SIR mode both the 3/16
th
or
the 1.6-
µ
s pulse duration methods are
supported. ACREG[7] selects the pulse-width method in transmit mode.
12.8.2.5
Encoder
Serial data from the transmit state machine is encoded to transmit data to the
optoelectronics (see Figure 12–15). While the serial data input to (TXD) is
high, the output (TXIR) is always low and the counter used to form a pulse on
TXIR is continuously cleared. After TXD resets to 0, TXIR rises on the falling
edge of the 7
th
16XCLK. On the falling edge of the 10
th
16XCLK pulse, TXIR
falls, creating a 3-clock-wide pulse. While TXD remains low, a pulse is trans-
mitted during the 7
th
to the 10
th
clocks of each 16-clock bit cycle.
Figure 12–15. IrDA Encoder Mechanism
TXD
1
2
4
5
6
3
7
8
10
11
12
9
13
14
16
15
16XCLK
TXIR
