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Chopperp

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Joined: 03/01/2018
Location: Australia
Posts: 1106

Posted: 11:58am 14 Apr 2018

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Hi
I can Write & Read single variables OK to the SD card using OPEN FOR RANDOM & SEEK. But I am having a great deal of trouble reading more than one variable from the card.
I also store lots of data OK with OPEN FOR APPEND, so I assume one would use OPEN FOR INPUT to get data back but I have nor worked out how to do it. It is obviously simple but I am missing the plot some where. I only want to read two variables back again.
Any help appreciated.
The Appendix on Random File I/O looks rather complicated for more than one variable or record.
(Give me 6502 machine code any day

)

Thanks

ChopperP

Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9750

Posted: 02:41am 15 Apr 2018

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You can keep your 6502 code!

Assuming you are reading and writing at random locations within a file on the card, then you would read back from the file using:

OPEN "FILE.TXT" FOR RANDOM AS #1 (for example) - See page 23 of the MM+ manual.

That done, use SEEK to position the file pointer within the file to the byte you want to start reading from: SEEK #1,200 for example.

Now, read the byte(s) at the pointer location: D$=INPUT$(5,#1), which will read in five bytes from byte 200, and stick them into D$ in this example. MMBASIC will increment the file pointer by however many bytes you want to read, but I THINK that the pointer will return to whatever you last set it to following the read - you would need to test that.

Smoke makes things work. When the smoke gets out, it stops!

Chopperp

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Joined: 03/01/2018
Location: Australia
Posts: 1106

Posted: 02:51am 15 Apr 2018

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Thanks Groggs. Will see if that works on the CMM later today.

ChopperP

Grogster

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Posts: 9750

Posted: 02:56am 15 Apr 2018

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Oh, I missed the bit about the CMM....

Hopefully though, SD card access is pretty standard across all the versions. (false logic?)

Smoke makes things work. When the smoke gets out, it stops!

Chopperp

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Joined: 03/01/2018
Location: Australia
Posts: 1106

Posted: 12:45pm 15 Apr 2018

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I knew it was easy but took a long while to get something working.
In a nutshell
Storing:
Open file for RANDOM AS # whatever
Seek #, position 1
Print Data1
Seek #, position 2
Print Data2
Close #

Retrieving:
open again
seek # position 1
input #, Data1
seek # position 2
input #, Data2
close #

ChopperP

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