RV-3029 Datasheet, PDF (29/67 Pages) MICORO CRYSTAL SWITZERLAND – DTCXO Temperature Compensated Real Time Clock

Micro Crystal
DTCXO Temperature Compensated Real Time Clock / Calendar Module
RV-3029
4.4. TIMER FUNCTION
The RV-3029 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
00h
Control_1
Clk/Int TD1
TD0 SROn EERE TAR
Bit
Symbol
6
TD1
5
TD0
2
TAR
1
TE
Value
00
01
10
11
0
1
0
1
Description
Timer Source Clock Frequency: 32 Hz
Timer Source Clock Frequency: 8 Hz
Timer Source Clock Frequency: 1 Hz
Timer Source Clock Frequency : 0.5 Hz
Disables Countdown Timer Auto-Reload mode
Enables Countdown Timer Auto-Reload mode
Disables Countdown Timer
Enables Countdown Timer
Bit 1
TE
Bit 0
WE
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”.
Register Countdown Timer (addresses 18h / 19h…bits description)
Register 18h is loaded with the low byte of the 16-bit Countdown Timer value ,n’
Register 19h is loaded with the high byte of the 16-bit Countdown Timer value ,n’
Address
18h
19h
Bit
18h
19h
Function
Timer Low
Timer High
Symbol
Timer Low
Timer High
Bit 7
128
128
Bit 6
64
64
Value
xx01 to xxFF
00xx to FFxx
Bit 5
32
32
Bit 4
16
16
Bit 3
8
8
Bit 2
4
4
Bit 1
2
2
Description
Countdown value = n
Countdown period
=
n
Source Clock Frequency
Bit 0
1
1
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