ST62T45B STMicroelectronics, ST62T45B Datasheet - Page 41

• Manufacturer Part Number: ST62T45B
• Description: 8-BIT OTP/EPROM MCU
• Manufacturer: STMicroelectronics

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TIMER 1& 2 (Cont’d)
4.2.1 TIMER 1 Operating Modes
There are three operating modes, which are se-
lected by the TOUT and DOUT bits (see TSCR
register). These three modes correspond to the
two clocks which can be connected to the 7-bit
prescaler (f
the output mode.
4.2.1.1 Gated Mode
(TOUT = “0”, DOUT = “1”)
In this mode the prescaler is decremented by the
Timer clock input (f
signal on the TIMER pin is held high (allowing
pulse width measurement). This mode is selected
by clearing the TOUT bit in the TSCR register to
“0” (i.e. as input) and setting the DOUT bit to “1”.
4.2.1.2 Event Counter Mode
(TOUT = “0”, DOUT = “0”)
In this mode, the TIMER pin is an input and the
prescaler is decremented on the rising edge.
4.2.1.3 Output Mode
(TOUT = “1”, DOUT = data out)
The TIMER pin is connected to the DOUT latch,
hence the Timer prescaler is clocked by the pres-
caler clock input (f
The user can select the desired prescaler division
ratio through the PS2, PS1, PS0 bits. When the
TCR count reaches 0, it sets the TMZ bit in the
TSCR. The TMZ bit can be tested under program
control to perform a timer function whenever it
goes high. The low-to-high TMZ bit transition is
used to latch the DOUT bit of the TSCR and trans-
fer it to the TIMER pin. This operating mode allows
external signal generation on the TIMER pin.
Table 14. Timer Operating Modes
TOUT
0
0
1
1
DOUT
INT
0
1
0
1
12 or TIMER pin signal), and to
Input
Input
Output
Output
INT
Timer Pin
INT
12).
12), but ONLY when the
Event Counter
Gated Input
Output “0”
Output “1”
Timer Function
4.2.2 TIMER 2 Operating Mode
The Timer prescaler is clocked by the prescaler
clock input (f
The user can select the desired prescaler division
ratio through the PS2, PS1, PS0 bits. When the
TCR count reaches 0, it sets the TMZ bit in the
TSCR. The TMZ bit can be tested under program
control to perform a timer function whenever it
goes high.
4.2.3 Timer Interrupt
When one of the counter registers decrements to
zero with the associated ETI (Enable Timer Inter-
rupt) bit set to one, an interrupt request is generat-
ed as described in Interrupt Chapter. When the
counter decrements to zero, the associated TMZ
bit in the TSCR register is set to one.
4.2.4 Application Notes
The user can select the presence of an on-chip
pull-up on the TIMER pin as option.
TMZ is set when the counter reaches zero; how-
ever, it may also be set by writing 00h in the TCR
register or by setting bit 7 of the TSCR register.
The TMZ bit must be cleared by user software
when servicing the timer interrupt to avoid unde-
sired interrupts when leaving the interrupt service
routine. After reset, the 8-bit counter register is
loaded with 0FFh, while the 7-bit prescaler is load-
ed with 07Fh, and the TSCR register is cleared.
This means that the Timer is stopped (PSI=“0”)
and the timer interrupt is disabled.
A write to the TCR register will predominate over
the 8-bit counter decrement to 00h function, i.e. if
a write and a TCR register decrement to 00h occur
simultaneously, the write will take precedence,
and the TMZ bit is not set until the 8-bit counter
reaches 00h again. The values of the TCR and the
PSC registers can be read accurately at any time.
INT
12).
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