Remote-processing RPC-52 Bedienungsanleitung PDF herunterladen (Seite 16)

RAM MEMORY CHAPTER 5

Page 14

Figure 5-2 RPBASIC-52 m emory map

RESERVING MEMORY

Normally, RPBASIC -52 uses the first 30K of RAM for

program and variable storage. However, additional

memory can be reserved for PEEK and POKE variables

using RPBASIC-52' s CON FIG MTOP statement.

When only a small number of variables need to be stored

(or a small assembly language program run), a 32K

RAM system may be adequate. If the combined

program and data size exceed 30K, a 128K or 512K

RAM is necessary. The additional RAM may be

necessary if your program has large arrays and/ or string

storage requirements.

The CONFIG MT OP statement is not necessary when

you do not use RPBA SIC-52 m emor y for var iable

storage. This is possible w hen a 128K o r 512K R AM is

installed. However, you may want to set MTO P to the

top of RAM using the CON FIG M TOP com mand.

Highest MTOP value is 65535.

STORING VARIABLES IN RAM

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

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

application.

Program s and RPBASIC-52 variables reside in segment

0. Var iables are generally stored in segment 1 and

higher (a segment is 64K of memory). See mem ory map

figure 5-2. "Extended memory" is segment 1 or higher.

PEEK and POKE commands store and retrieve values

from memory. For example:

20 POKE B1,12,A

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

Use the PEEK statement to retrieve the variable:

50 B = PEEKB(1,12)

You can store and retrieve strings and variab les in this

way. There are many variations of PEEK and POKE

statements. Refer to the RPBASIC-52 Software

Supplement in this manual for additional information and

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

chapter.

CORRUPTED VARIABLES

The RPC -52' 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 susceptib le to corr uption. This is

especially true when the board is powered down. The

RPC-52 has an intelligent reset circuit which minimizes

data corruption. However, when POKEing long data,

such as strings, a reset could interr upt a saving process.

The result is information is corrupted.

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 and strings.

On power up, your program should compare values from

one set to the other one or two. If the two (or three)

agree, then there was no corruption and the program can

reliably use the values. At run time, 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 are then re-initialized.

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

that the data in the first set is valid.

Data is written to each 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 (POKE' d) 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.

Upon reset, the calibration value is checked. If the value

at address 0 agrees with address 100 and 200, then no

corruption occurred. When address 0 and 100 agree but

not 200, then this indicates that a reset occurre d at while

updating the third set. The first data set can be trusted.

The third data set simply needs to be updated.

When the first two sets do not agree, then you know that

the first data is corrupted. If the second and third set

agree, then, depending upon the system r equireme nts,

the first set could be "corrected" using the old data. The

user or other device could be alerted that a calibration

(or whatever) must be performed again. When all three

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