MAXQ61CA MAXIM [Maxim Integrated Products], MAXQ61CA Datasheet - Page 14

• Manufacturer Part Number: MAXQ61CA
• Description: 16-Bit Microcontroller with Infrared Module
• Manufacturer: MAXIM [Maxim Integrated Products]

The IR timer is composed of a carrier generator and a
carrier modulator. The carrier generation module uses
the 16-bit IR carrier register (IRCA) to define the high
and low time of the carrier through the IR carrier high
byte (IRCAH) and IR carrier low byte (IRCAL). The carrier
modulator uses the IR data bit (IRDATA) and IR modula-
tor time register (IRMT) to determine whether the carrier
or the idle condition is present on IRTX.
The IR timer is enabled when the IR enable bit (IREN) is
set to 1. The IR Value register (IRV) defines the begin-
ning value for the carrier modulator. During transmission,
the IRV register is initially loaded with the IRMT value
and begins down counting towards 0000h, whereas
in receive mode it counts upward from the initial IRV
register value. During the receive operation, the IRV
register can be configured to reload with 0000h when
capture occurs on detection of selected edges or can be
allowed to continue free-running throughout the receive
operation. An overflow occurs when the IR timer value
rolls over from 0FFFFh to 0000h. The IR overflow flag
(IROV) is set to 1 and an interrupt is generated if enabled
(IRIE = 1).
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
• Carrier Frequency (f
• 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.
16-Bit Microcontroller with Infrared Module
14
IRCAL + 2)
_____________________________________________________________________________________
IRCLK
Carrier Generation Module
) = f
CARRIER
SYS
/2
) = f
IRDIV[1:0]
IRCLK
/(IRCAH +
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
IRTX pin is set to a logic-high when the IR timer module is
enabled. If IRTXPOL = 0, the IRTX pin is set to a logic-low
when the IR timer is enabled.
A separate register bit, IR data (IRDATA), is used to
determine whether the carrier generator output is output
to the IRTX pin for the next IRMT carrier cycles. When
IRDATA = 1, the carrier waveform (or inversion of this
waveform if IRTXPOL = 1) is output on the IRTX pin dur-
ing the next IRMT cycles. When IRDATA = 0, the idle
condition, as defined by IRTXPOL, is output on the IRTX
pin during the next IRMT cycles.
The IR timer acts as a down counter in transmit mode. An
IR transmission starts when the IREN bit is set to 1 when
IRMODE = 1; when the IRMODE bit is set to 1 when IREN
= 1; or when IREN and IRMODE are both set to 1 in the
same instruction. The IRMT and IRCA registers, along
with the IRDATA and IRTXPOL bits, are sampled at the
beginning of the transmit process and every time the IR
timer value reload its value. When the IRV reaches 0000h
value, on the next carrier clock, it does the following:
1) Reloads IRV with IRMT.
2) Samples IRCA, IRDATA, and IRTXPOL.
3) Generates IRTX accordingly.
4) Sets IRIF to 1.
5) Generates an interrupt to the CPU if enabled (IRIE = 1).
To terminate the current transmission, the user can
switch to receive mode (IRMODE = 0) or clear IREN to 0.
Carrier Modulation Time = IRMT + 1 carrier cycles
IR Transmission