ST62E01C ST Microelectronics, ST62E01C Datasheet - Page 37

• Manufacturer Part Number: ST62E01C
• Description: (ST62T00C / ST62T01C / ST62T03C / ST62E01C) 8-BIT OTP/EPROM MCUs
• Manufacturer: ST Microelectronics

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 2
Figure 24 shows the Timer Block Diagram. The
content of the 8-bit counter can be read/written in
the Timer/Counter register, TCR, which can be ad-
dressed in Data space as a RAM location at ad-
dress 0D3h. The state of the 7-bit prescaler can be
read in the PSC register at address 0D2h. The
control logic device is managed in the TSCR reg-
ister as described in the following paragraphs.
The 8-bit counter is decrement by the output (ris-
ing 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. If the ETI (Enable Timer Inter-
rupt) bit in the TSCR is also set, an interrupt re-
quest is generated. The Timer interrupt can be
used to exit the MCU from WAIT mode.
Figure 24. Timer Block Diagram
f
INT
12
PSC
6
5
4
3
2
1
0
8
SELECT
1 OF 7
15
.
COUNTER
DATA BUS
3
8-BIT
The prescaler input is the internal frequency (f
divided by 12. The prescaler decrements on the
rising edge. Depending on the division factor pro-
grammed by PS2, PS1 and PS0 bits in the TSCR
(see Figure 11), the clock input of the timer/coun-
ter register is multiplexed to different sources. For
division factor 1, the clock input of the prescaler is
also that of timer/counter; for factor 2, bit 0 of the
prescaler register is connected to the clock input of
TCR. This bit changes its state at half the frequen-
cy of the prescaler 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 register must be set to allow the prescaler
(and hence the counter) to start. If it is cleared, all
the prescaler bits are set and the counter is inhib-
ited from counting. The prescaler can be loaded
with any value between 0 and 7Fh, if bit PSI is set.
The prescaler tap is selected by means of the
PS2/PS1/PS0 bits in the control register.
Figure 25 illustrates the Timer’s working principle.
8
ST62T00C/T01C ST62T03C/E01C
TMZ ETI D5
b7 b6
STATUS/CONTROL
b5
REGISTER
D4 PSI PS2 PS1 PS0
b4
8
b3 b2
b1
INTERRUPT
b0
LINE
VR02070A
37/70
INT
37
)