参数资料
型号: ST72774S9T1/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PQFP44
封装: TQFP-44
文件页数: 81/144页
文件大小: 1280K
代理商: ST72774S9T1/XXX
ST72774/ST727754/ST72734
41/144
4.3 16-BIT TIMER (TIM)
4.3.1 Introduction
The timer consists of a 16-bit free-running counter
driven by a programmable prescaler.
It may be used for a variety of purposes, including
pulse length measurement of up to two input
signals (
input capture) or generation of up to two
output waveforms (
output compare and PWM).
Pulse lengths and waveform periods can be
modulated from a few microseconds to several
milliseconds using the timer prescaler and the
CPU clock prescaler.
4.3.2 Main Features
s
Programmable prescaler: fcpu divided by 2, 4 or
8.
s
Overflow status flag and maskable interrupt
s
External clock input (must be at least 4 times
slower than the CPU clock speed) with the
choice of active edge
s
Output compare functions with
– 2 dedicated 16-bit registers
– 2 dedicated programmable signals
– 2 dedicated status flags
– 1 dedicated maskable interrupt
s
Input capture functions with
– 2 dedicated 16-bit registers
– 2 dedicated active edge selection signals
– 2 dedicated status flags
– 1 dedicated maskable interrupt
s
Pulse width modulation mode (PWM)
s
One pulse mode
s
5 alternate functions on I/O ports*
The Block Diagram is shown in Figure 27.
Note: Some external pins are not available on all devices.
Refer to the device pin out description.
4.3.3 Functional Description
4.3.3.1 Counter
The principal block of the Programmable Timer is a
16-bit free running counter and its associated 16-
bit registers:
Counter Registers
– Counter High Register (CHR) is the most sig-
nificant byte (MSB).
– Counter Low Register (CLR) is the least sig-
nificant byte (LSB).
Alternate Counter Registers
– Alternate Counter High Register (ACHR) is the
most significant byte (MSB).
– Alternate Counter Low Register (ACLR) is the
least significant byte (LSB).
These two read-only 16-bit registers contain the
same value but with the difference that reading the
ACLR register does not clear the TOF bit (overflow
flag), (see note page 43).
Writing in the CLR register or ACLR register resets
the free running counter to the FFFCh value.
The timer clock depends on the clock control bits
of the CR2 register, as illustrated in Table 15 Clock
Control Bits. The value in the counter register
repeats every 131.072, 262.144 or 524.288
internal processor clock cycles depending on the
CC1 and CC0 bits.
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