David Hawkins wrote:
Hi Jerry,
I have limited CFI experience, but my flash experience is that the flash chips ignore extra bytes in the data lanes when you send commands. Assuming your flash isn't bit-swapped, you should be able to write the magic bytes down all four byte lanes and have it work for byte-wide, 16-bit-wide, and 32-bit-wide chips or paralleled 8-bit or 16-bit wide chips. This neatly solves the byte swap issue as well.
Nice to know, thanks.
The other critical part is the address you use. Depending on the width of your chip(s) and if more than one paralleled on the bus, you will have to add zero "0" bits to the magic 55 / AA addresses in the manual.
For the translation of byte-wide to 16 bit wide: 55 (0101_0101) becomes 0AA (0_1010_1010) AA (1010_1010) becomes 254 (1_0101_0100) ^ added '0' bit
For the translation of byte-wide to 32 bit wide: 55 (0101_0101) becomes 154 (01_0101_0100) AA (1010_1010) becomes 2A8 (10_1010_1000) ^^ two added '0' bits
Ooh, thats a sneaky one.
I think (hope) the Spansion chips are 'smarter' than that. They have a BYTE# pin that configures it to operate in 8-bit (low) versus 16-bit (high), and in byte mode DQ15 become A-1 (address bit minus -1). I'm pretty sure the Spansion data sheet describes the commands in terms of byte addresses, so there is no ambiguity of byte versus 'word' (which has so many meanings ...) addresses in the command codes.
Robert has correctly connected the Flash address and data signals, so he shouldn't have to massage the address/data relative to the data sheet command codes.
I'm pretty sure the Altera FPGA boards that I ran some tests on used Spansion Flash, and I didn't have to shift the address part of the Flash command.
Nice info though, thanks. Dave
The address shifting happens when the hardware guys put down (2) 8-bit flash chips to be 16 bits wide, (4) 8-bit flash chips to be 32 bits wide, or (2) 16-bit flash chips to be 32 bits wide. Size, timing, availability, and cost reasons usually drive this (and the first three are weighted very low).
Back when we had to subtract two '1' bits to make '0's, flashes (actully, EEPROMs to really show my age) only came in 8 bit wide packages so the address shifting phenomena happened quite often.
gvb