I wonder if this is another issue affecting particular brands of SD cards.
It's a shame manufacturers don't release datasheets.

Here is another spec sheet I was able to pull up.
http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Components/General/SDSpec.pd=
f

Hope this helps,
Robert

----------------------------------------
> Date: Sun, 8 Mar 2015 00:12:16 +1300
> From: joecolquitt@clear.net.nz
> Subject: [PIC] Resuming SDHC block reads
> To: piclist@mit.edu
>
> Hi all,
>
> I have a problem resuming block reads on an SDHC card
>
> When the card is being initialised, part of that process is that a PIC
> reads the card's FAT and puts copies of the each file's start cluster
> and length into two tables. The number of the file to be retrieved is
> sent from another PIC. The PIC managing the card fetches its start
> cluster and length from the two tables using the file number as an
> index. It then gets the blocks from the card under a timer interrupt
> until the block count (file length) has been reached. I'm not using
> "multiple read.
>
> So far so good
>
> However - if I try to read another file it doesn't work. Only if I
> re-initialise the card (which doesn't involve re-reading the FAT)
> allows me to access another file. Unfortunately this can take up
> to 1/2 second which causes a real hiccup downstream. in the
> PIC which uses the data
>
> The documentation I've been using is generally this one
>
> https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_301.p=
df
>
> I haven't found any mention of eg a time-out for data reading and
> assumed that CMD17 can be sent any time to access any block
>
> Can anyone offer a clue as to why accessibility of other files seems
> to halt at the end of reading another ? I'm sure there's something
> I've left out or not doing wuite right. The data from the file read is
> fine BTW
>
> TIA
>
> Joe
>
>
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