Greetings Erik Maas...
EM>Before you can write a byte into Flash memory, you have to write
>a special byte sequence to different addresses.
That's true for the older style of Flash, such as made by Catalyst.
Atmel Flash chips don't require a special byte sequence to write
data into them -- other than writing a block (page) of bytes, and
allowing for the time-delay of the internal programming process.
Quoting directly from the Atmel data book, re their AT29C256...
"PROGRAM: The device is reprogrammed on a page basis. If a byte
of data within a page is to be changed, data for the entire page
must be loaded into the device. Any byte that is not loaded
during the programming of its page will be erased to FFh. Once
the bytes of a page are loaded into the device, they are simul-
taneously programmed during the internal programming period. After
the first data byte has been loaded into the device, successive
bytes are entered in the same way, Each new byte to be programmed
must have its high-to-low transition on /WE (or /CE) within 150us
of the low-to-high transition of /WE (or /CE) of the preceding byte.
If a low-to-high transition is not detected within 150us of the last
low-to-high transition, the load period will end and the internal
programming period will start. A6 to A14 specify the page address.
The page address must be valid during each high-to-low transition
of /WE (or /CE). A0 to A5 specify the byte address within the page.
The bytes may be loaded in any order, sequential loading is not
required."
The maximum write-cycle time, for the AT29C256, is 10ms.
EM>So, Flash is defenitly not just like (slow) RAM.
Contemporary Flash technology, as described above, certainly is
like slow RAM.
Suitable for data and code storage, but not a stack-pointer!
Cheers,
Greg_
http://www.netcom.ca/~telic
1998.Oct.09, Toronto, Canada
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