Remote-processing RPC-220 Manuel d'utilisateur télécharger pdf (Page 28)

REAL TIME CLOCK SECTION 7

Page 7-3

Step by step instructions are:

Screen Description

MP a00a<Enter> Your entry to access

A00A 20 31 Indicates oscillator off. Enter

31 for 256 Hz, select extended

registers. Press space bar.

A00B 03 0a<Enter> Set register B to 0A.

This enables square wave

and 24 hr mode.

MP a04b Select extended control

A04B 40 20< Enter> Indicates 32768 output.

Enter 20 for crystal bit at

12.5 pF, disable 32Khz

output, enable square

wave.

Other registers are accessed similarly. See RTC-1. C for

program example that accesses m ost of the registers.

OTHER REGISTERS

The DS1689 has a fe w reg isters that m ay be of inter est.

See demonstration code in RTC -1.C for access

examples.

There are two kinds of elapsed tim e counters. The first

one, located at 0xa054 - 0xa057, bank 1, counts elapsed

time power has been applied. The second counter

located at 0xA058 - 0xa05B records the total number of

seconds the clock has been running, both battery and

external powered supplied.

These counters may be useful for determining when

equipment needs maintenance, end of battery life, or

other similar situations. Since these are easily read and

reset, they can be used as second ary tim ers for relatively

long events.

A power cycle counter at addresses 0xa05c-0xa05d, bank

1, counts the num ber of tim es power is applied. This

can also be useful for maintenance alerts.

Each card with a RTC has a unique 64 bit serial number

located at addresses 0xa040 - 0xa47, bank 1. You can

embed this serial num ber into your code to uniquely

identify a system and prevent unauthorized copying.

EXTERNAL BATTERY

The batter y included on tw o RPC -220 ver sions is, in

theory, good for 10 years of power off backup.

practice, you will achieve 4 to 6 years of life. This is

true of any lithium button cell. F actors that cause life to

decrease are elevated temperatures, high and low

humidity. A batteries' self discharge doubles w hen its

envir on me nt t em pe ra tur e cha ng es fr om 25°C t o 50°C .

This alone reduces battery life from 10 years to 5.

Lower temperatures reduce self discharge rate.

Low humidity pr omotes the evapor ation of electr olyte

from the battery. H igh humidity helps dischar ge it.

If battery life is not long enough, you may connect an

external 3 volt battery at W7. You must remove the

existing battery first. A Tadiran

model TL-5276/ SL is

a utility meter battery and will, in theory, provide

backup for over 100 years.

Battery current is about 1.5 micro-amps with board

power off.

Remote Processing can build versions without the battery

and with W7 installed. Minimum quantities will apply.

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.

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Remote-processing RPC-220 Manuel d'utilisateur Page 28

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