m41t83 STMicroelectronics, m41t83 Datasheet - Page 38

• Manufacturer Part Number: m41t83
• Description: Serial I 2c Bus Rtc With Battery Switchover
• Manufacturer: STMicroelectronics

3.8
3.8.1
Note:
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8-bit (countdown) timer
The Timer Value Register is an 8-bit binary countdown timer. It is enabled and disabled via
the Timer Control Register (11h) TE bit. Other timer properties such as the source clock, or
interrupt generation are also selected in the Timer Control Register (see
accurate read back of the countdown value, the I
frequency of at least twice the selected timer clock.
The Timer Control register selects one of four source clock frequencies for the timer (4096,
64, 1, or 1/60Hz), and enables/disables the timer. The timer counts down from a software-
loaded 8-bit binary value. At the end of every countdown, the timer sets the Timer Flag (TF)
bit. The TF bit can only be cleared by software. When asserted, the timer flag (TF) can also
be used to generate an interrupt (IRQ1/FT/OUT) on the M41T83. The interrupt may be
generated as a pulsed signal every countdown period or as a permanently active signal
which follows the condition of TF. The Timer Interrupt/Timer Pulse (TI/TP) bit is used to
control this mode selection. When reading the timer, the current countdown value is
returned.
Table 9.
1. Bit positions labeled with ‘0’ should always be written with logic '0.
Timer interrupt/timer pulse (TI/TP, M41T83 only)
●
●
If an Alarm condition, Watchdog time-out, Oscillator Failure, or OUT = 0 causes
IRQ1/FT/OUT to be asserted low, then IRQ1/FT/OUT will remain asserted even if TI/TP is
set to '1'. When in pulse mode (TI/TP = 1), clearing the TF bit will not stop the pulses on
IRQ1/FT/OUT. The output pulses will only stop if TE, TIE, or TI/TP are reset to '0'.
Addr
0Fh
10h
11h
TI/TP = 0
IRQ1/FT/OUT is active when TF is logic '1' (subject to the status of the Timer Interrupt
Enable bit (TIE).
TI/TP = 1
IRQ1/FT/OUT pulses are active when TF is logic '1' according to
the status of the TIE bit).
WDF
D7
TE
Timer control register map
TI/TP
AF1
D6
AF2
TIE
D5
Timer countdown value
D4
BL
0
(1)
D3
TF
0
2
C-bus clock (SCL) must be operating at a
OF
D2
0
'
TD1
D1
0
TD0
D0
0
Table 10
Table
Timer control
Timer value
Function
9). For
(subject to
Flags