st62t62cmae STMicroelectronics, st62t62cmae Datasheet - Page 43
Manufacturer Part Number
8-bit Otp/eprom/fastrom Mcus With A/d Converter, Safe Reset, Auto-reload Timer And Eeprom
4.3 AUTO-RELOAD TIMER
The Auto-Reload Timer (AR Timer) on-chip pe-
ripheral consists of an 8-bit timer/counter with
compare and capture/reload capabilities and of a
7-bit prescaler with a clock multiplexer, enabling
the clock input to be selected as f
external clock source. A Mode Control Register,
ARMC, two Status Control Registers, ARSC0 and
ARSC1, an output pin, ARTIMout, and an input
pin, ARTIMin, allow the Auto-Reload Timer to be
used in 4 modes:
– Auto-reload (PWM generation),
– Output compare and reload on external event
– Input capture and output compare for time meas-
– Input capture and output compare for period
The AR Timer can be used to wake the MCU from
WAIT mode either with an internal or with an exter-
nal clock. It also can be used to wake the MCU
from STOP mode, if used with an external clock
signal connected to the ARTIMin pin. A Load reg-
ister allows the program to read and write the
counter on the fly.
4.3.1 AR Timer Description
The AR COUNTER is an 8-bit up-counter incre-
mented on the input clock’s rising edge. The coun-
ter is loaded from the ReLoad/Capture Register,
ARRC, for auto-reload or capture operations, as
well as for initialization. Direct access to the AR
counter is not possible; however, by reading or
writing the ARLR load register, it is possible to
read or write the counter’s contents on the fly.
The AR Timer’s input clock can be either the inter-
nal clock (from the Oscillator Divider), the internal
clock divided by 3, or the clock signal connected to
the ARTIMin pin. Selection between these clock
sources is effected by suitably programming bits
CC0-CC1 of the ARSC1 register. The output of the
AR Multiplexer feeds the 7-bit programmable AR
Prescaler, ARPSC, which selects one of the 8
available taps of the prescaler, as defined by
PSC0-PSC2 in the AR Mode Control Register.
Thus the division factor of the prescaler can be set
to 2n (where n = 0, 1,..7).
The clock input to the AR counter is enabled by the
TEN (Timer Enable) bit in the ARMC register.
When TEN is reset, the AR counter is stopped and
the prescaler and counter contents are frozen.
When TEN is set, the AR counter runs at the rate
of the selected clock source. The counter is
cleared on system reset.
The AR counter may also be initialized by writing
to the ARLR load register, which also causes an
immediate copy of the value to be placed in the AR
counter, regardless of whether the counter is run-
ning or not. Initialization of the counter, by either
method, will also clear the ARPSC register, where-
upon counting will start from a known value.
4.3.2 Timer Operating Modes
Four different operating modes are available for
the AR Timer:
Auto-reload Mode with PWM Generation. This
mode allows a Pulse Width Modulated signal to be
generated on the ARTIMout pin with minimum
Core processing overhead.
The free running 8-bit counter is fed by the pres-
caler’s output, and is incremented on every rising
edge of the clock signal.
When a counter overflow occurs, the counter is
automatically reloaded with the contents of the Re-
load/Capture Register, ARCC, and ARTIMout is
set. When the counter reaches the value con-
tained in the compare register (ARCP), ARTIMout
On overflow, the OVF flag of the ARSC0 register is
set and an overflow interrupt request is generated
if the overflow interrupt enable bit, OVIE, in the
Mode Control Register (ARMC), is set. The OVF
flag must be reset by the user software.
When the counter reaches the compare value, the
CPF flag of the ARSC0 register is set and a com-
pare interrupt request is generated, if the Compare
Interrupt enable bit, CPIE, in the Mode Control
Register (ARMC), is set. The interrupt service rou-
tine may then adjust the PWM period by loading a
new value into ARCP. The CPF flag must be reset
by user software.
The PWM signal is generated on the ARTIMout
pin (refer to the Block Diagram). The frequency of
this signal is controlled by the prescaler setting
and by the auto-reload value present in the Re-
load/Capture register, ARRC. The duty cycle of
the PWM signal is controlled by the Compare Reg-