ST72652 View Datasheet(PDF) - STMicroelectronics
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ST72652 Datasheet PDF : 166 Pages
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ST7265x
11.4 16-BIT TIMER
11.4.1 Introduction
The timer consists of a 16-bit free-running counter
driven by a programmable prescaler.
11.4.2 Main Features
s Programmable prescaler: fCPU divided by 2, 4 or 8.
s Overflow status flag and maskable interrupt
s Output compare functions with
– 2 dedicated 16-bit registers
– 2 dedicated programmable signals
– 2 dedicated status flags
– 1 dedicated maskable interrupt
s 2 alternate functions on I/O ports (OCMP1,
OCMP2)
The Block Diagram is shown in Figure 45.
11.4.3 Functional Description
11.4.3.1 Counter
The main block of the Programmable Timer is a
16-bit free running upcounter and its associated
16-bit registers. The 16-bit registers are made up
of two 8-bit registers called high & low.
Counter Register (CR):
– Counter High Register (CHR) is the most sig-
nificant byte (MS Byte).
– Counter Low Register (CLR) is the least sig-
nificant byte (LS Byte).
Alternate Counter Register (ACR)
– Alternate Counter High Register (ACHR) is the
most significant byte (MS Byte).
– Alternate Counter Low Register (ACLR) is the
least significant byte (LS Byte).
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 (Timer
overflow flag), located in the Status register, (SR),
(see note at the end of paragraph titled 16-bit read
sequence).
Writing in the CLR register or ACLR register resets
the free running counter to the FFFCh value.
Both counters have a reset value of FFFCh (this is
the only value which is reloaded in the 16-bit tim-
er).
The timer clock depends on the clock control bits
of the CR2 register, as illustrated in Table 27 Clock
Control Bits. The value in the counter register re-
peats every 131.072, 262.144 or 524.288 CPU
clock cycles depending on the CC[1:0] bits.
The timer frequency can be fCPU/2, fCPU/4, fCPU/8
or an external frequency.
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