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ADSP-21375 - 1Mbit SRAM ?

Started by BitCrusher July 18, 2007
Hello,

I was wondering if anyone else noticed that the Analog Devices ADSP-21375 
seems to have 1 Mbit of SRAM.

When you look at early ldf-files for the 21375 it claims that the 21375 has 
1 Mbit of SRAM and the address ranges were:

//   Block 0   0x0009 8000 to 0x0009 9FFF  Normal word (32) Space (0.25 Mbit 
RAM)
//   Block 1   0x000B 8000 to 0x000B 9FFF  Normal word (32) Space (0.25 Mbit 
RAM)
//   Block 2   0x000C 0000 to 0x000C 1FFF  Normal word (32) Space (0.25 Mbit 
RAM)
//   Block 3   0x000E 0000 to 0x000E 1FFF  Normal word (32) Space (0.25 Mbit 
RAM)

In the latest VDSP 4,5 update the memory map for the 21375 was changed 
(corrected ldf-files, reduced memory spaces). Also the manuals/spec sheets 
for the 21375 mention only 0.5 Mbit internal SRAM.

However, my tests showed that the 21375 has 4 x 0.25 Mbit blocks of SRAM 
(old ldf-file memory spaces are correct) and it's all usable!


I asked the AD support and they sort of confirm that there might be SRAM in 
the "reserved memory space" but they strongly recommend not to use it. Maybe 
the first revision of the chip has 1 Mbit SRAM and the future revisions will 
be reduced to half?


Thanks!
Joerg


BitCrusher wrote:
> I asked the AD support and they sort of confirm that there might be SRAM in > the "reserved memory space" but they strongly recommend not to use it. Maybe > the first revision of the chip has 1 Mbit SRAM and the future revisions will > be reduced to half? >
I'm not terrible familiar with the varieties of this family, but perhaps they test the memory at the factory, and if there are failures in the upper half-meg, they mark the part a a half-meg device. Just a supposition. -- Jim Thomas Principal Applications Engineer Bittware, Inc jthomas@bittware.com http://www.bittware.com (603) 226-0404 x536 The secret to enjoying your job is to have a hobby that's even worse - Calvin's Dad
Jim Thomas wrote:
> BitCrusher wrote: >> I asked the AD support and they sort of confirm that there might be >> SRAM in the "reserved memory space" but they strongly recommend not to >> use it. Maybe the first revision of the chip has 1 Mbit SRAM and the >> future revisions will be reduced to half? >> > > I'm not terrible familiar with the varieties of this family, but perhaps > they test the memory at the factory, and if there are failures in the > upper half-meg, they mark the part a a half-meg device. > > Just a supposition.
Some very early 2K EPROMs came in two styles. For one, you used what would have been A0 through A9 and A10 of a 4K device, while for others, you used A0-A9 and A11. Later, when the chips were tested before being packaged, the change was done in the wire bonding and all parts used A0-A10 externally. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯