September 1999, Issue 110

Get Smart Media—(Part 1):
What's It All About?

528 – 512 = 16

Here’s where we learn about those 16 extra bytes in each page. Because manufacturing these large-scale NAND flash memory arrays is difficult, there’s the possibility of having a defective cell in one or more pages. A cell may also deteriorate during its life of over a quarter million programming cycles.

The extra 16 cells are a way of keeping track of bad pages, like bad sectors on magnetic media. When the SmartMedia is tested after manufacturing, if a bad page is found, a 00H is written to the sixth extra byte of the last 16 bytes of the page (the other 15 bytes are erased to 0FFH ). Be advised that when a block is erased, so are the bad page identifiers, so you must either keep track externally and rewrite the indicators back after erasing, or pay attention to the status register.

The status register can be read by issuing a command 70H and then reading back the status byte (after 60 µs). Three of the eight bits are significant. Bit 0 indicates a program/erase success by a bit value of 0 and by a failure of 1. An erase failure indicates all bits within the block could not be erased to an erased FFH state.

A program failure indicates that at least one byte’s bit within the page could not be programmed to a 0. From this information, you can update that page’s invalid page indicator so it won’t be used in the future.

In addition, Bit 6 is a software indication of the hardware ready/busy output—0 when busy and 1 when ready. Bit 7 is software indication of the protect status, 0 indicating protected and 1 indicating not protected.

The protection status is an input pin to the SmartMedia. A low on this pin protects the flash memory from being erased or programmed. The user may place an adhesive conductive dot on the SmartMedia as an indication that the device is read-only. This conductive dot is read by a pair of contacts on the SmartMedia socket and must be interpreted by your hardware.