A newbie question

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I am reading the compact flash card specification, and I have some really
newbie questions:

"Data Register (Address - 1F0h[170h]; Offset 0, 8, 9)"

So what does the value 170h inside of the square bracket represent? I think
1F0h is already enough for an address, right?

What do those 3 offsets represent? The data register is only one register,
and why does it need 3 offsets?

Maybe it sounds too stupid for you, but no laugh allowed ....

Thanks in advance.


Re: A newbie question
On Thu, 2 Dec 2004 14:48:29 -0700, "Johnson Liuis"

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The 1f0 and 170 represent "port numbers" in a PC or such. If you ask
the question in the context of an embedded system (which I asume here)
these numbers are completely without any meaning. The data register is
at address '0' and is also mirrored at address 8 & 9 relative to the
place in the address room you operate the CF in. Wether you call this
"ofset" or "address" depends on how you build the address (i.e. if you
bitbang it, if you hook it up to a potentially present address &
databus etc.).



Re: A newbie question
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Right. But the 170h address is for the slave (=second) device on the IDE
The offset is simply the offset from the base address. So offset 8 is simply
1F8h. Why this is done: you refer to all registers with a construct like
BASE+1 or BASE+2, so you only have to change one single definition of BASE
to change your code from accessing the master to the slave device.


Re: A newbie question
Thanks, Meindert,

Do you know why they provide 3 offsets (Offset 0, 8, 9)  instead of only one
(Offset 0)? What is the benefit?


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Re: A newbie question
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These three offsets actually point to different I/O addresses of the IDE
interface. Liek I explained, 1F0 is the base, so with the offsets 0, 8 and 9
you actually address ports 1F0, 1F8 and 1F9. Each of these addresses is a
different register in the IDE interface (data port, cylinder number, sector
number etc.).


Re: A newbie question
Thanks, Meindert,

Here I copied the texts from the "CF+ and CompactFlash Specification
Revision 2.1".

"Data Register (Address - 1F0h[170h]; Offset 0, 8, 9)"
"The Data Register is a 16 bit register, and it is used to transfer data
blocks between the
CompactFlash Storage Card data buffer and the Host. This register overlaps
the Error Register.

Table 37: Data Register Access below describes the combinations of data
register access and is

provided to assist in understanding the overlapped Data Register and
Error/Feature Register

rather than to attempt to define general PCMCIA word and byte access modes
and operations.

See the PCMCIA PC Card Standard, for further definitions of the Card
Accessing Modes for I/O

and Memory cycles.

Note: Because of the overlapped registers, PC Card modes access to the 1F1h,
171h or offset 1 are not

defined for word (-CE2 = 0 and -CE1 = 0) operations. These accesses are
treated as accesses to the

Word Data Register. The duplicated registers at offsets 8 and 9 have no
restrictions on the

operations that can be performed by the socket."

See it looks like the offsets 8 and 9 are copies of the offset 0, am I


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Re: A newbie question
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I think what this means is that the data register can be accessed as a 16
bit word only at offset 0 and that offsets 8 and 9 can be used to
individually access the high and low byte of the data register.


Re: A newbie question

SanDisk provides good documentation: try www.sandisk.com and look in
the "industriy" area.

The company I work for is building modules to read Compact Flash Memory
Cards over a serial connection ( RS232 ). All the Compact Flash driver
and file system stuff is on board. You read and write files through
simple "AT" commands.

This certainly simplifies live.
Take a look at www.avisaro.com


Avisaro AG

Re: A newbie question
Thanks a lot, Meindert and Markus.


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