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DATA MEMORY CHAPTER 5

Page 14 RPC-2300

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 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 other ) must be performed again. W hen all thre e sets

disagree, then you must take action appropriate to the

situation.

Another technique to ch eck for valid mem ory is

checksum s. Sim ply write a progr am to add the values in

RAM and compare it against a number is a good check.

However, you cannot tell which data element was

corrupted.

Instances of data corruption are rar e. T hey do increase

as the board power is cycled or reset.

ASSEMBLY LANGUAGE INTERFACE

Assembly language programs (including compiled C)

must start from segment 0. Use the CAM BASIC II

CALL statement to execute an assembly language

program.

A specific area of RAM should be reserved for the

program. This is to prevent strings and variables from

corrupting that area of RAM . Use the SYS(1) and

SYS(2) statements to do this. SYS(1) returns the low_wt

memory location while SYS(2) returns the upper

location. Run the program first to make sure variable

memory has been allocated before running these SYS

commands. F ailure to do so may r esult in address

returned that are not really free for assembly language

program s.

There are sever al ways to put a program in mem ory,

depending upon your application.

1. Use DATA statements and POKE the code into

segment 0 RAM.

2. Write a program to download code. Some

applications are connected to a larger system which

"initializes" its systems. Using INKEY $ or COM $,

code is received and then poked into memory using

POKE$.

3. Read the code from the EPROM (U3) (using INP)

and transfer it to RAM (using POKE).

4. Some space is available in the CAMBASIC II

ROM . Space from about 6C00H to 7F FFH is

available in ver sion 1.0. T he starting address w ill

probably change in the future with different

CAMBASIC II versions. Y ou may burn your

assembly language pr ogram in U1 and CAL L in

from BASIC.

In all cases, it is best to load code into RAM from a

"secure" source. E ven though RAM is battery backed,

over time there is the possibility it could be corrupted.

Below is an example of loading and running an asse mbly

language program.

100 FOR N = &FB00 TO &FB0C

110 READ A

120 POKE N,A

130 NEXT

900 DATA &DB, 2, &47, &E6, &FE, &D3

910 DATA 2, &78, &F6, 1, &D3, 2, &C9

2000 CALL &FB00

Lines 100 to 130 load the program into RAM. DATA

statements may be entered manually or made by the

MAKED B program included with PC SmartLINK.

Line 2000 calls the program listed below. It toggles J2

line 13.

IN A,(2)

LD B,A

AND 0FEH

OUT (2),A

LD A,B

OR 1

OUT (2),A

RET

COMMANDS

The following is a list of CAMBASIC II commands used

with RAM.

Command Function

CALL Calls an assembly language routine

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 35 36

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