Remote Processing RPC-210 - Manual (Page 36)

REAL TIME CLOCK BASIC SECTION 7
Page 7-2
STABILITY AND TEMPERATURE
R e al ti m e c lo c k' s c r y st a l i ni ti a l t ol e ra n ce is ±2 0 pp m .
(Toleranc e is specified as
) f/f.) This tolerance changes
due to the following factors: Temperatur e, 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
t e mp e r at ur e c oe f fi c ie n t i s - 0 . 03 5 pp m / °C .
Another factor that causes the clock to run faster is very
high humidity. When m oisture 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 cr ystal with a non -conductive sealant.
IDLE AND POWER DOWN MODES
The RP C-210 c an powe r dow n to a state re quiring on ly
20 micro-Am ps. 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: R u nn in g a p o we r p ro g r am , s u ch a s R T C -
2.BAS, could cause the board to be powered
off. When you go back and tr y to run the
board, it appears d ead. To get ar ound this
problem, either bring P1-5 (“ P” ) to ground or
bring in pow er to P 1-2 (“ E” ). W hat is
happening is the board is in power down mode
and must be woken up.
Your progr am can autorun o n 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 micr o-Amps.
6 to 16V DC pow er 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. T hese
registers can, w hen other registers are progr ammed,
wake up the car d from its lowest pow er mode . T hese
alarms and description are on page 6 of the DS1689-
93.P DF data sheet. See demo program RTC-2. BAS for
sample program ming.
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
register. The board will then wake up when the alarm
registers match. You could program the board to wake
up ever y 5 minutes , for example , by simply
repr ogram ming the m inutes alarm register for the ne xt 5
minute interval. You can do the same for seconds and
hours.
Powering external devices
When the RPC -210 is in pow er dow n 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 tw o 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
procee ds to the next com mand af ter 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 interr upt need only c onsist 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 NF IG BAU D 1, .. . state ment m ust have pr eviously
been executed and the board set up to receive characters
before IDLE 1 will work here.