Remote-processing RPC-30 Uživatelský manuál stáhnout pdf (Strana 19)

CHAPTER 5 RAM MEMORY

RPC-30 Page 17

Battery voltage is between 2.5 and 3.3 volts. T he

voltage is measured by placing a volt meter between

ground and the battery clip.

The battery may be replaced by the following type or

equivalent:

Panasonic BR2325

To replace the battery, lift up the holder and push the

battery from behind. To install, simply reverse the

procedure. The batter y may be replaced while pow er is

on. If you replace the batter y with power off, be sure to

reset the date and time. Also, data stored in RAM will

be lost.

STORING VARIABLES IN RAM

The term "var iables" in this context includes numb ers,

strings, arrays, recipes, and formulas as applied to your

application.

Progr ams and C AMBASIC variables reside in the first

64K of RAM called segment 0. Your variables are

generally stored in segment 1 and higher.

PEEK and POKE commands store and retrieve values

from memory. For example:

20 POKE 12,A,1

puts the value of A into segment 1, address 12.

Use the PEEK statement to retrieve the variable:

50 B = PEEK(12, 1)

You can store and retrieve arrays, strings, and variables

in this way. There ar e many variations of PEE K and

POKE statements. Refer to the CAMBA SIC

Programming Manual for additional information and

examples. A list of comm ands appea rs at the end of this

chapter.

CORRUPTED VARIABLES

The RPC -30' s RAM is automatically battery backed up.

User defined data can be saved when the board is

powered off then on. W hen your application m ust rely

on the accuracy of this data after power up, corrupted

variables becomes a possibility.

The nature of RAM is it is easily written to. Any

POKE' d data is susceptible to corr uption. This is

especially true when the board is powered down. The

RPC-30 has an intelligent reset circuit which minimizes

data corruption. However, when POKEing long data,

such as strings and floating point numbers, a reset could

interrupt a saving pr ocess. The r esult is inform ation is

corrupted. A scenario is explained below.

A program is running and POKEing data into RAM. At

the same time it is poking, a reset occurs. A reset can

occur due to power loss, someone pushing the reset

button, or a wa tchdog time r time out.

If the program was POKEing a string (POKE $), floating

point number (FPOKE), double byte (DPOKE ), or arr ay

while the reset occurred, the data became corrupted.

This is because the complete value was not saved.

Since it is impossible to predict or delay a reset, a work

around is to duplicate or triplicate POKEd values. That

is, you would have to save the same information in two

or three different places. F or purposes of discussion,

POKEd variables are called sets because data can consist

of a mixture of variables, strings and arrays.

On power up, the program compares values from one set

to the other one or two. If the two (or three) agreed,

then there was no corruption and the program can

reliably use the values. In practice, you would read

information from set 1, but would save data to all two or

three.

The use of duplicate or triplicate sets depends upon what

the system must or can do if data is corrupted. When

using a duplicate set, a corrupted set indicates that

default values (from serial EEPROM or the program)

should be used, since it is uncertain if the first or second

set is corrupted. Both data sets would then be re-

initialized.

A triplicate set is used to recover the last set or indicate

that the data in the first set is valid. The pr ocedure and

logic is as follows.

Data is written to each element in a set in a specific and

consistent order (data to an entire set does not have to be

written to, just that element). For example, a calibration

constant is saved (POKEd) in three different places.

Assume that the constant was assigned address 0, 100,

and 200 in segment 1. The data is POKEd to address 0

first, then 100, then 200.

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 37 38

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