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8bitwizard wrote:Normal TTL data level is like 0.2V low and 2.8V high, which is why 3.3V became a standard. There shouldn't be a problem as long as you can get a voltage converter for the 3.3V power.

It' true, standard TTL use only approx 2,6v as log.1. And WIKI says:

All standardized common TTL circuits operate with a 5-volt power supply. A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2.2 V and 5 V[12] (precise logic levels vary slightly between sub-types). TTL outputs are typically restricted to narrower limits of between 0 V and 0.4 V for a "low" and between 2.6 V and 5 V for a "high", providing 0.4V of noise immunity.

But, there are CMOS "TTL". CMOS logic can output almost Vcc at log.1, wich can be more, than 4,5V if Vcc=5V. So, there are strongly reccomended to use level shifter or just limit current by resistor between TTL and LTTL(LVTTL) devices. In practic, 75..100 ohm resistor are best. And, as Shiru says:

Shiru wrote:Some 3V ICs are 5V-tolerant. There are level convertors as well. In one of Flash carts (for SMD) schematics I recall was used 3V Flash with a lot of resistors to convert the levels. Here is the schematics of the cartridge (bottom part of page 3).

There are 5V signal tolerant 3,3V devices. They don't require any level shifters or converters, but still require 3,3V as power source. For example, MAX3000A CPLD's are 5V tolerant, but use 3,3V as Vcc. So, just RTFM. :3

Ok...5v->3.3v on VCC and level shifter or resistors on any pins but VCC & GND
thanks!

Since I'm working on memory again, I bump this topic to add another question :

from what I read, Flash memory need command to write data like
Load AA to address 5555
Load 55 to address 2AAA
Load A0 to address 5555
Load Data
(not clear if I had to do it for each byte or for a full sector)

which make it difficult (and slow!) to use in a Flash cart....
It could make sense on a "full" cart but not on a rewritable one...

Does standard eeprom also need this program command sequence ?
I saw flash cart firmware which don't use this sequence...

This JEDEC discribed unlock sequence is valid only for NOR based FLASH. And only for protection from accidentally data corruption (obviously, very tiny probability for accidentally change address and data lines in chess order, even in broken software). EEPROM uses serial interface, wich handle some protection, wich reduces accidentally data corruption by wrong command.
And one more thing: there are two different unlock modes discribed in JEDEC. First - byte based. This means you must apply unlock sequence for every written byte. Second - page based. This means you can write more than one byte after unlock sequence. Usually, page has 2^n bytes (128, 256 etc.), I saw 128 bytes page programming in some 39Fxxxx FLASHes. Ofcourse page based programming are faster. So read datasheet carefully, if you want to increase writing speed. Maybe, your FLASH can handle page programming.
As for writing speed - that's why I want tru RAM based universal cartrige with some boot code and MMC/SD card support.

Problem is when you search for eeprom, you always find Flash (with this sequence protection)....

KanedaFr wrote:Problem is when you search for eeprom, you always find Flash (with this sequence protection)....

Technically all FLASHes are EEPROM (Electrically Erasable Programmable Read Only Memory). But in fact, all NOR-based and NAND-based EEPROMs are called FLASH and Serial EEPROMs called EEPROMs. Maybe you must slightly change your search request?

Ok, I finally found some interesting model like the AT28C040...it has the sequence protect commands but you need to enable it (disabled by default)