Epson S1C17704, Техническое руководство

Страница: 140 / 423

11 16-BIT TIMERS (T16)
11-2
EPSON
S1C17704 TECHNICAL MANUAL
11.2 16-bit Timer Operating Mode
The 16-bit timer has three operating modes.
1. Internal clock mode (general timer to count the internal clock)
2. External clock mode (functions as an event counter)
3. Pulse width measurement mode (measures external input pulse widths by counting the internal clock)
Use CKSL[1:0] (D[9:8]/T16_CTL x register) to select the operating mode.
∗
CKSL[1:0] : Input Clock and Pulse Width Count Mode Select Bits in the 16-bit Timer Ch. x Control (T16_CTL x )
Register (D[9:8]/0x4226/0x4246/0x4266)
Table 11.2.1 Selecting Operating Mode
CKSL[1:0] Operating mode
0x3 Reserved
0x2 Pulse width measurement mode
0x1 External clock mode
0x0 Internal clock mode
(Default: 0x0)
11.2.1 Internal Clock Mode
In internal clock mode, the timer uses the prescaler output clock as the count clock.
The timer starts counting down from the counter initial value set in the reload data register and outputs the
underflow signal when the counter underflows. The underflow signal is used to generate an interrupt and a clock
for the internal serial interface. The period until an underflow occurs can be programmed minutely according to the
prescaler clock and counter initial value selections, so this mode is useful for generating a serial transfer clock or a
one-shot time measurement.
Selecting the count clock
Use the DF[3:0] bits (D[3:0]/T16_CLK x register) to select the count clock from the 15 clocks, PCLK divided
by 1 to PCLK divided by 16K, generated by the prescaler.
∗
DF[3:0] : Timer Input Clock Select Bits in the 16-bit Timer Ch. x Input Clock Select (T16_CLK x ) Register
(D[3:0]/0x4220/0x4240/0x4260)
Table 11.2.1.1 Selecting the Count Clock
DF[3:0] Prescaler output clock DF[3:0] Prescaler output clock
0xf Reserved 0x7 PCLK•1/128
0xe PCLK•1/16384 0x6 PCLK•1/64
0xd PCLK•1/8192 0x5 PCLK•1/32
0xc PCLK•1/4096 0x4 PCLK•1/16
0xb PCLK•1/2048 0x3 PCLK•1/8
0xa PCLK•1/1024 0x2 PCLK•1/4
0x9 PCLK•1/512 0x1 PCLK•1/2
0x8 PCLK•1/256 0x0 PCLK•1/1
(Default: 0x0)
Notes : • Before the 16-bit timer can start counting in internal clock mode, the prescaler must be run.
• When setting the count clock, make sure the 16-bit timer counter is stopped.
For controlling the prescaler, see Chapter 9, “Prescaler (PSC).”