Remote-processing RPC-210 Manual de usuario descargar pdf (Pagina 36)

REAL TIME CLOCK BASIC SECTION 7

Page 7-2

STABILITY AND TEMPERATURE

Real time clock's crystal initial tolerance is ±20 ppm.

(Tolerance is specified as )f/f.) This tolerance changes

due to the following factors: Temperature, hum idity, and

operating environm ent.

Reference temperature is 25 °C. F requency drift is an

additional 40 ppm at -10°C and + 60°C. Peak

temperature coefficient is -0.035 ppm/°C.

Another factor that causes the clock to run faster is very

high humidity. When moisture condenses on the board,

there is an increase of apparent capacitance. Increased

capacitance causes the crystal to oscillate at a higher

frequency.

When the operating environment is dirty, or contains

conductive "dust", the crystal can change frequency.

A way to prevent these problems is to coat the areas

around the clock crystal with a non-conductive sealant.

IDLE AND POWER DOWN MODES

The RP C-210 can power down to a state requiring only

20 micro-Amps. The boar d is “waked up” by bringing

P1-’P’ or J7-20 to ground or by programming the clock

to turn on power at a specific time.

An external device may be used to wake up the board.

This control to P1-‘P’ or J7-20 should be an open

collector device or a relay. A TTL com patible + 5V line

may also be used. Do not exceed + 5V at these pins.

NOTE: Running a power program, such as RTC-

2.BAS, could cause the board to be powered

off. When you go back and try to run the

board, it appears dead. To get ar ound this

problem, either bring P1-5 (“P”) to ground or

bring in pow er to P1-2 (“ E” ). W hat is

happening is the board is in power down mode

and must be woken up.

Your program can autorun on power up (Set J7-17 to

ground). Som etimes it is useful to know if power up

was a result of the clock or external stimulus (at P1-’P’).

The program RTC-2.BAS detects when the clock alarm

powered up the board and allows you to set the date and

time to power the board back up. Current dr aw during

power dow n standby is about 20 micro-Amps.

6 to 16V DC power is applied to the ‘B’ terminal on P1.

Ground is applied to the ‘G’ terminal. Install jumpers

into W7 and W8.

There is a set of alar m register s in the clock. These

registers can, when other registers are progr ammed,

wake up the card from its lowest pow er mode. These

alarms and description are on page 6 of the DS1689-

93.PDF data sheet. See demo program RTC-2. BAS for

sample programming.

Briefly described, you can put the card in lowest power

mode and wake up at either/or a specific second, minute,

hour, or day of month interval. Each alarm is disabled

by writing a value greater than 0c0H to the desired

registers match. You could program the board to wake

up every 5 minutes , for example, by simply

reprogram ming the m inutes alarm register for the next 5

minute interval. You can do the same for seconds and

hours.

Powering external devices

When the RPC -210 is in power down mode, power to

external devices can also be turned off. Simply power

your devices from the “ E” or “5" terminal. W hen the

board is powered on, battery voltage appears at the “E”

terminal and + 5V at the “5" term inals.

IDLE Command

There are two variations of the IDLE comm and.

IDLE (or IDL E 0) keeps the car d at full power. Use

this command to wait for any interrupt. When the

interrupt is received, the subroutine will be processed.

When returning from the subroutine, the program

proceeds to the next com mand after ID LE. When this

version of IDLE is executing, tick timers are still active.

IDLE 1 can be used to save about 50 mA of power and

still wait for serial or ITR 0 interrupts only. The CPU

effectivly shuts down during this time.

A CO M 0 ser ial interrupt need only consist of one single

character. An ON C OM statement will not, by it self,

break out of IDLE 1. The sam e is true with COM 1.

A CO NFIG BAU D 1, .. . statement m ust have pr eviously

been executed and the board set up to receive characters

before IDLE 1 will work here.

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Remote-processing RPC-210 Manual de usuario Pagina 36

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