参数资料
型号: ST62E85BG1
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, UVPROM, 8 MHz, MICROCONTROLLER, CQFP80
封装: CERAMIC, QFP-80
文件页数: 35/78页
文件大小: 868K
代理商: ST62E85BG1
Obsolete
Product(s)
- Obsolete
Product(s)
40/78
ST62T85B/E85B
4.2 TIMER
The MCU features an on-chip Timer peripheral,
consisting of an 8-bit counter with a 7-bit program-
mable prescaler, giving a maximum count of 215.
The peripheral may be configured in three different
operating modes.
Figure 20 shows the Timer Block Diagram. The
external TIMER pin is available to the user. The
content of the 8-bit counter can be read/written in
the Timer/Counter register, TCR, while the state of
the 7-bit prescaler can be read in the PSC register.
The control logic device is managed in the TSCR
register as described in the following paragraphs.
The 8-bit counter is decremented by the output
(rising edge) coming from the 7-bit prescaler and
can be loaded and read under program control.
When it decrements to zero then the TMZ (Timer
Zero) bit in the TSCR is set to “1”. If the ETI (Ena-
ble Timer Interrupt) bit in the TSCR is also set to
“1”, an interrupt request is generated as described
in the Interrupt Chapter. The Timer interrupt can
be used to exit the MCU from WAIT mode.
The prescaler input can be the internal frequency
fINT divided by 12 or an external clock applied to
the TIMER pin. The prescaler decrements on the
rising edge. Depending on the division factor pro-
grammed by PS2, PS1 and PS0 bits in the TSCR.
The clock input of the timer/counter register is mul-
tiplexed to different sources. For division factor 1,
the clock input of the prescaler is also that of tim-
er/counter; for factor 2, bit 0 of the prescaler regis-
ter is connected to the clock input of TCR. This bit
changes its state at half the frequency of the pres-
caler input clock. For factor 4, bit 1 of the PSC is
connected to the clock input of TCR, and so forth.
The prescaler initialize bit, PSI, in the TSCR regis-
ter must be set to “1” to allow the prescaler (and
hence the counter) to start. If it is cleared to “0”, all
the prescaler bits are set to “1” and the counter is
inhibited from counting. The prescaler can be
loaded with any value between 0 and 7Fh, if bit
PSI is set to “1”. The prescaler tap is selected by
means of the PS2/PS1/PS0 bits in the control reg-
ister.
Figure 21 illustrates the Timer’s working principle.
Figure 20. Timer Block Diagram
DATABUS 8
8
8-BIT
COUNTER
6
5
4
3
2
1
0
PSC
STATUS/CONTROL
REGISTER
b7
b6
b5
b4
b3
b2
b1
b0
TMZ ETI
TOUT
DOUT
PSI
PS2
PS1
PS0
SELECT
1 OF 7
3
LATCH
SYNCHRONIZATION
LOGIC
TIMER
INTERRUPT
LINE
VA00009
:12
fOSC
40
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