7480 Group and 7481 Group User's Manual
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1.12 Timer X and Timer Y
HARDWARE
Reads from Timers
When the high-order byte of an operating timer is read, the low-order byte is set in the latch for
reading. Therefore, the read value of the low-order byte retains the value at the time the high-order
byte is being read.
In the count operation, the contents of each timer are decremented by 1 at every rising edge of
the count source, while the contents of each timer are transferred to the latch for reading by falling
edge, so that the read value of the timer may be different from its real value.
Figure 1.12.28 shows an operation in timer X or timer Y at reads.
Figure 1.12.28 Operation in Timer X or Timer Y at Reads
(2)
In Event Count Mode
The inverted signal of input to a CNTR pin is used as the count source when a CNTR edge selection
bit of the edge polarity selection register is ‘1’.
Keep the frequency of the CNTR pin input used as the count source f(XIN)/4 or less.
(3)
In Pulse Output Mode
When the timer X or Y write control bit is ‘0’, the CNTR pin output is initialized to the following levels
by a write to the timer:
HIGH when the CNTR edge selection bit is ‘0’.
LOW when the CNTR edge selection bit is ‘1’.
When the timer X or Y write control bit, however, is ‘1’, the CNTR pin output level cannot be
initialized by a write to the timer.
The output level of a CNTR pin is inverted when the CNTR edge polarity selection bit is switched.
(4)
In Pulse Period Measurement Mode and Pulse Width Measurement Mode
Do not write to timers in these modes; otherwise the last measured value in the timer latch will be
changed by this write.
When a timer is read, the read value is the contents of the timer latch (the last measured value).
(5)
In Programmable Waveform Generation Mode
When the timer X or Y operation mode bits, which are set to other modes, are switched to the
programmable waveform generation mode, the CNTR pin outputs are initialized to LOW.
When the timer X or Y trigger selection bit is ‘1’, keep the trigger widths input to the INT pins 250ns
or more.
Count source
High-order of timer is read (Read value: ‘0116’)
In this case, the low-order read value ‘0116’ is
written to latch for reading.
Low-order of timer is read (Read value: ‘0116’)
Contents of timer
Read value of timer
010016
00FF16
00FE16
010116
010216
010016
00FF16
00FE16
00FD16
010116