Rainbow Electronics MAXQ613 - Manual (Page 15)

16-Bit Microcontroller with Infrared Module
MAXQ613
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Carrier Generation Module
The IRCAH byte defines the carrier high time in terms of
the number of IR input clocks, whereas the IRCAL byte
defines the carrier low time.
• IR Input Clock (f
IRCLK ) = f SYS /2 IRDIV[1:0]
• Carrier Frequency (f CARRIER ) = f IRCLK /(IRCAH +
IRCAL + 2)
• Carrier High Time = IRCAH + 1
• Carrier Low Time = IRCAL + 1
• Carrier Duty Cycle = (IRCAH + 1)/(IRCAH + IRCAL + 2)
During transmission, the IRCA register is latched for
each IRV down-count interval, and is sampled along with
the IRTXPOL and IRDATA bits at the beginning of each
new IRV down-count interval so that duty-cycle variation
and frequency shifting is possible from one interval to the
next, which is illustrated in Figure 1.
Figure 2 illustrates the basic carrier generation and its
path to the IRTX output pin. The IR transmit polarity bit
(IRTXPOL) defines the starting/idle state and the carrier
polarity of the IRTX pin when the IR timer is enabled.
IR Transmission
During IR transmission (IRMODE = 1), the carrier gen-
erator creates the appropriate carrier waveform, while
the carrier modulator performs the modulation. The car-
rier modulation can be performed as a function of carrier
cycles or IRCLK cycles dependent on the setting of the
IRCFME bit. When IRCFME = 0, the IRV down counter is
clocked by the carrier frequency and thus the modula-
tion is a function of carrier cycles. When IRCFME = 1, the
IRV down counter is clocked by IRCLK, allowing carrier
modulation timing with IRCLK resolution.
The IRTXPOL bit defines the starting/idle state as well as
the carrier polarity for the IRTX pin. If IRTXPOL = 1, the
Figure 1. IR Transmit Frequency Shifting Example (IRCFME = 0)
CARRIER OUTPUT
(IRV)
IRDATA
IR INTERRUPT
0 1
IRMT = 3
0
IRTX
IRTXPOL = 1
IRTX
IRTXPOL = 0
IRCA
IRMT IRMT = 5
IRCA = 0202h IRCA = 0002h
IRCA, IRMT, IRDATA SAMPLED AT END OF IRV
DOWN-COUNT INTERVAL
3 1 2 0 5 4 3 2 1 0