Remote-processing RPC-2350 Manuel d'utilisateur télécharger pdf (Page 31)

CHAPTER 5 DATA MEMORY

5-5

several things happen. Data saved at line 1000 is

overwritten by the data in line 2000, even though

different write addresses were specified. This brings us

to the second r eason sector size is impor tant.

CAM BASIC forces the requested Flash address down to

an even sector addr ess. In both cases above, data is

written to the Flash starting at address 0, not at 5 or 42.

The easiest way to m ake an even sector address is to

“A ND ” the Flash ad dress w ith &FF80 (as is done in

ARRAY2.BAS program exam ple) when using a 128K

flash or &FF00 with a 512K.

Another consideration is the number of times Flash can

be written to. A tmel specifies anywhere from 1000 to

10,000 or m ore writes. Compared to R AM, this is quite

limiting. Flash should be used to stor e default constants

or data that changes only occasionally.

Writing takes about 90 ms/1000 bytes. During SAVE

time, interrupts (ON COM$, ON KEYPAD, ON BIT,

etc.. ) are rec ognized but not serviced. If these

comm ands must be serviced quicker , w rite data in

smaller blocks.

Using LOAD to transfer data

The LOAD comm and can be used to transfer data from

Flash to RAM or RAM to RAM. Use SAVE to transfer

from RAM to Flash.

LOAD transfers up to 64K blocks of memory at a time.

Use it to transfer an entire data structure containing

recipes, formulas, constants, etc.

The sample program ARRAY3. BAS shows how to move

data from extended memory RAM into CAMBASIC and

back.

INSTALLING 512K RAM

A 512K RAM (part num ber 103 9) can be installe d in

U2. The addition al RAM allows you to increase data

storage, not program size.

Follow these steps to install RAM.

1. Turn off power to the board.

2. Remove existing IC from U 2.

3. Install the 512K RAM . M ake sure pin 1 is

oriented towards the board edge. Pin 1 will be

marked with a dot or notch on top.

4. Move jumper W2[1-2] to [2-3].

You are now ready to power up the board. You can

now PEE K and POKE data into segments 1-7.

CORRUPTED VARIABLES

When your application must r ely on the acc uracy o f data

after power up, corrupted variables become 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. U26

monitors the supply voltage and turn s off wr iting when it

is below about 4.65 volts. However, when POKE ing

long data, such as strings and floating point numbers, or

writing to Flash, a power down could interrupt a saving

process. The result is information is corrupted. A

scenario is explained below.

A program is running and saving data. During this time

a reset occurs. A reset can occur due to power loss,

someone pushing the reset button, or a watchdog timer

time out. The data is c orru pted because the com plete

value was not saved.

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

around is to duplicate or triplicate values. That is, you

would have to save the same information in two or three

different places. Usually you only need to save the

pointers to data structures.

When you are w riting ar rays of data (such as show n in

LOG GER .BAS), the sequence your pr ogram should

follow is this: Write data to RAM. Update the pointer.

This pointer could be in duplicate or triplicate. This

way, you only loose one set of data.

When you are saving only one set of data, the following

applies.

For purposes of discussion, data variables are called sets

because it can consist of a mixture of variables, strings

and arrays.

On power up, your program would compare 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

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Remote-processing RPC-2350 Manuel d'utilisateur Page 31

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