RV-3049 datasheet(29/65 Pages) MICROCRYSTAL

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Micro Crystal

DTCXO Temperature Compensated Real Time Clock / Calendar Module

RV-3049

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4.4. TIMER FUNCTION

The RV-3049 offers different Alarm and Timer functions which allow simply generating highly versatile timing-

functions.

The Countdown Timer is controlled by the register Control_1. Bit 1 “TE” enables the Timer function; bits 5 & 6

“TD0” and “TD1” determine one of 4 Timer Source Clock frequencies (32 Hz, 8 Hz, 1 Hz, or 0.5Hz).

The Timer counts down from a software-loaded 16-bit binary value ,n’, “Timer Low” (bit 0-7 at address 18h) and

“Timer High” (bit 0-7 at address 19h). Values, n’ from 1 to 65536 are valid; loading the counter with ,n’ = “0”

effectively stops the timer. The end of every Timer countdown is achieved when the Timer Counter value ,n’

reaches = “0”.

Countdown Timer can be set in Automatic Reload mode by “TAR” = “1” (bit 2 of register Control_1), the counter

automatically re-loads Timer countdown value, n’ and starts the next Timer period. Automatic reload of the

countdown value ,n’ requires 1 additional timer source clock. This additional timer source clock has no effect on the

first Timer period, but it has to be taken into account since it results in a Timer duration of ,n+1’ for subsequent

timer periods.

The generation of Interrupts from the Countdown Timer function is enabled by “TIE” = “1” (bit 1 in register

Control_INT). If Timer Interrupt is enabled by “TIE” = “1”, the Timer Flag “TF” (bit 1 in register Control_INT Flag) will

be set = “1” at the end of every Timer countdown. The Interrupt signal INT follows the condition of Timer Flag “TF”

(bit 1 in register Control_INT Flag), the INT signal can be cleared by clearing the “TF” = “0”.

Control of the Countdown Timer Functions (address 00h…bits description)

Address

Function

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

00h

Control_1

Clk/Int

TD1

TD0

SROn

EERE

TAR

Bit

Symbol

Value

Description

TD1

Timer Source Clock Frequency: 32 Hz

Timer Source Clock Frequency: 8 Hz

TD0

Timer Source Clock Frequency: 1 Hz

Timer Source Clock Frequency : 0.5 Hz

TAR

Disables Countdown Timer Auto-Reload mode

Enables Countdown Timer Auto-Reload mode

Disables Countdown Timer

Enables Countdown Timer

The Timer Source Clock Frequency “TD0” & “TD1” and the Timer Auto Reload mode “TAR” can only be written

when the Timer is stopped by “TE” = “0” (bit 1 in register Control_1).

The Countdown Timer values in “Timer Low” and “Timer High” can only be written when the Timer is stopped by

“TE” = “0” and Timer Auto Reload mode is disabled “TAR” = “0”.

Address

Function

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

18h

Timer Low

128

19h

Timer High

128

Bit

Symbol

Value

Description

18h

Timer Low

xx01 to xxFF

Countdown value = n

Countdown period

Frequency

Clock

Source

19h

Timer High

00xx to FFxx

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