参数资料
型号: ST6375B1/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, PDIP42
封装: SHRINK, PLASTIC, DIP-42
文件页数: 25/84页
文件大小: 861K
代理商: ST6375B1/XXX
31/84
ST6365, ST6375, ST6385 ST6367, ST6377, ST6387
4.2 TIMERS
The ST638x devices offer two on-chip Timer pe-
ripherals consisting of an 8-bit counter with a 7-bit
programmable prescaler, thus giving a maximum
count of 2
15, and a control logic that allows config-
uration the peripheral operating mode. Figure 20
shows the Timer block diagram. The content of the
8-bit counters can be read/written in the Timer/
Counter registers TCR that are addressed in the
data space as RAM locations at addresses D3h
(Timer 1), DBh (Timer 2). The state of the 7-bit
prescaler can be read in the PSC register at ad-
dresses D2h (Timer 1) and DAh (Timer 2). The
control logic is managed by TSCR registers at D4h
(Timer 1) and DCh (Timer 2) addresses as de-
scribed in the following paragraphs.
The following description applies to all Timers. The
8-bit counter is decrement 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 one. If the ETI (enable timer in-
terrupt) bit in the TSCR is also set to one an inter-
rupt request, associated to interrupt vector #3 for
Timer 1 and #1 for Timer 2, is generated. The in-
terrupt of the timer can be used to exit the MCU
from the WAIT mode.
The prescaler decrements on rising edge. The
prescaler input is the oscillator frequency divided
by 12. Depending on the division factor pro-
grammed by PS2/PS1/PS0 (see Table 11) bits in
the TSCR, the clock input of the timer/counter reg-
ister is multiplexed to different sources. On divi-
sion factor 1, the clock input of the prescaler is
also that of timer/counter; on factor 2, bit 0 of pres-
caler register is connected to the clock input of
TCR.
This bit changes its state with the half frequency of
prescaler clock input. On factor 4, bit 1 of PSC is
connected to clock input of TCR, and so on. On di-
vision factor 128, the MSB bit 6 of PSC is connect-
ed to clock input of TCR. The prescaler initialize bit
(PSI) in the TSCR register must be set to one to al-
low the prescaler (and hence the counter) to start.
If it is cleared to zero then all of the prescaler bits
are set to one and the counter is inhibited from
counting.The prescaler can be given any value be-
tween 0 and 7Fh by writing to the related register
address, if bit PSI in the TSCR register is set to
one. The tap of the prescaler is selected using the
PS2/PS1/PS0 bits in the control register. Figure 21
illustrates the Timer working principle.
Figure 20. Timer Peripheral 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 8
3
LATCH
SYNCHRONIZATION
LOGIC
TIMER
INTERRUPT
LINE
VA00009
:12
fOSC
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