NEC mPD789425, User Manual

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CHAPTER 6 16-BIT TIMER
User’s Manual U15075EJ1V0UM00
129
6.5 Notes on Using 16-Bit Timer
Usable functions differ according to the settings of the count clock selection, CPU clock operation, system clock
oscillation status, and BZOE90 (bit 0 of buzzer output control register 90 (BZC90)).
Refer to the following table.
System Clock Count
Clock
CPU
Clock
Main System Clock Subsystem Clock
BZOE90 Capture TM90
Read
Buzzer
Output
Timer
Output
Timer
Interrupt
Oscillating
√ √
Note 1
Note 2
√ √
Main
Stopped
Oscillating/Stopped
× × × × ×
Oscillating
√ ×
Note 2
√ √
f
X
/2
2
,
f
X
/2
6
,
f
X
/2
7
Sub
Stopped
Oscillating
1/0
× × × × ×
0
√ √ × √ √
Oscillating
1
× × √ √ √
Oscillating
Stopped 1/0
× × × × ×
0
× × × × ×
Oscillating
1
× × √ √ √
Main
Stopped
(STOP mode)
Stopped 1/0
× × × × ×
0
√ √ × √ √
Oscillating
1
× × √ √ √
0
× × × × ×
f
XT
Sub
Stopped
Oscillating
1
× × √ √ √
Notes 1. TM90 is enabled only when the CPU clock is in high-speed mode.
2. Output is enabled when BZOE90 = 1.
Cautions 1. The capture function uses f
X
/2 for control (refer to Figure 6-1 Block Diagram of 16-Bit
Timer). Therefore, the capture function cannot be used when the main system clock is
stopped.
2. The read function of TM90 uses the CPU clock for control (refer to Figure 6-1), and reads an
undefined value when the CPU clock is slower than the count clock (values are not
guaranteed). When reading TM90, set the count clock to the same speed as the CPU clock
(when the CPU clock is the main system clock, high-speed mode is set), or select a clock
slower than the CPU clock.
3. When the subsystem clock is selected as the count clock and BZOE90 is set to 0, the
subsystem clock selected as the TM90 count clock is one that has been synchronized with
the main system clock (refer to Figure 6-1). Therefore, when the main system clock
oscillation is stopped, the timer operation is stopped because the clock supplied to the 16-
bit timer is stopped (timer interrupt is not generated).
Moreover, when the subsystem clock is selected as the count clock and BZOE90 is set to 1,
the capture and TM90 read values are not guaranteed because the subsystem clock is not
synchronized. Therefore, be sure to set BZOE90 to 0 when using the capture and TM90
read functions (when the subsystem clock is selected as the count clock, buzzer output,
capture, and TM90 read functions cannot be used at the same time).