MAXQ610_11 Datasheet, PDF (17/29 Pages) Maxim Integrated Products – 16-Bit Microcontroller with Infrared Module 1.70V to 3.6V Operating Voltage Range

16-Bit Microcontroller with Infrared Module
On the next qualified event, the IR module does the
following:
1) Captures the IRRX pin state and transfers its value to
IRDATA. If a falling edge occurs, IRDATA = 0. If a
rising edge occurs, IRDATA = 1.
2) Transfers its current IRV value to the IRMT.
3) Resets IRV content to 0000h (if IRXRL = 1).
4) Continues counting again until the next qualified
event.
If the IR timer value rolls over from 0FFFFh to 0000h
before a qualified event happens, the IR timer overflow
(IROV) flag is set to 1 and an interrupt generated if
enabled. The IR module continues to operate in receive
mode until it is stopped by switching into transmit mode
(IRMODE = 1) or clearing IREN = 0.
Carrier Burst-Count Mode
A special mode reduces the CPU processing burden
when performing IR learning functions. Typically, when
operating in an IR learning capacity, some number of
carrier cycles are examined for frequency determina-
tion. Once the frequency has been determined, the IR
receive function can be reduced to counting the number
of carrier pulses in the burst and the duration of the
combined mark-space time within the burst. To simplify
this process, the receive burst-count mode (as enabled
by the RXBCNT bit) can be used. When RXBCNT = 0,
the standard IR receive capture functionality is in place.
CARRIER FREQUENCY
CALCULATION
IRMT = PULSE COUNTING
IRV = CARRIER CYCLE COUNTING
IRMT = PULSE COUNTING
IRRX
IRV
IRMT
12346
7
8
5
9
CAPTURE INTERRUPT (IRIF = 1).
1 TO 4 IRV ≥ IRMT.
IRV = 0 (IF IRXRL = 1).
SOFTWARE SETS IRCA = CARRIER FREQUENCY.
SOFTWARE SETS RXBCNT = 1 (WHICH CLEARS IRMT = 0001 IN HARDWARE).
5 SOFTWARE CLEARS IRCFME = 0 SO THAT IRV COUNTS CARRIER CYCLES. IRV IS RESET TO 0 ON QUALIFIED EDGE DETECTION IF IRXRL = 1.
SOFTWARE ADDS TO IRMT THE NUMBER OF PULSES USED FOR CARRIER MEASUREMENT.
IRCA x 2x COUNTER FOR SPACE CAN BEGIN IMMEDIATELY (QUALIFIED EDGE RESETS).
6
QUALIFIED EDGE DETECTED: IRMT++
IRV RESET TO 0 IF IRXRL = 1.
IRCA x 2 PERIOD ELAPSES: IRIF = 1; CARRIER ABSENCE = SPACE.
7 BURST MARK = IRMT PULSES.
SOFTWARE CLEARS RXBCNT = 0 SO THAT WE CAPTURE ON THE NEXT QUALIFIED EDGE.
8 QUALIFIED EDGE DETECTED: IRIF = 1, CAPTURE IRV ≥ IRMT AS THE BURST SPACE (PLUS UP TO ONE CARRIER CYCLE).
9
SOFTWARE SET RXBCNT = 1 AS IN (5).
CONTINUE (5) TO (8) UNTIL LEARNING SPACE EXCEEDS SOME DURATION. IRV ROLLOVERS CAN BE USED.
Figure 6. Receive Burst-Count Example
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