Has anybody taken any special precautions when attaching 5V logic devices to the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any ADSP design) I've got an LCD (see newbie question earlier) which has a 5V interface to a Toshiba T6963 controller (later I'm going to use a SED1352 I think) and also other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals. I think I can get away with the 3.3V logic levels being able to trigger the logic 0 and 1 thresholds of the 5V system so long as I use the ADSP to drive into the 5V peripheral. It's the opposite direction though? 5V -> 3V? Is it best to use a FET transistor level shifter? 5V_|\|_____|\|___|-----|___ |/| |/| |_____| | | | ------- ^ | | | 5V system--- ------ 3V system One signal diode and one shottky diode giving a total voltage drop of about 2V? Does anyone recommend a better method or maybe a level converter chip/driver that I can buffer the output of the DSP data/address bus with? Thanks Pete |
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3.3V to 5V connectivity ?
Started by ●January 30, 2001
Reply by ●January 31, 20012001-01-31
3.3V -> 5V: works without level shifter 5V -> 3.3V: use 74LVCxx Best regards! Ralf Heuser-Lindner >Has anybody taken any special precautions when attaching 5V logic devices to >the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any >ADSP design) |
Reply by ●January 31, 20012001-01-31
Hi ! The 74ALVT_ family from Phillis Semiconductors should do the job The 74ALVT16244 is a high-performance BiCMOS product designed for VCC operation at 2.5V or 3.3V with I/O compatibility up to 5V. Regards sigurdm email: > ---------- > From: > Sent: Tuesday, January 30, 2001 8:51 AM > To: > Subject: [adsp] 3.3V to 5V connectivity ? > Has anybody taken any special precautions when attaching 5V logic > devices to > the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related > to any > ADSP design) > > I've got an LCD (see newbie question earlier) which has a 5V > interface to a > Toshiba T6963 controller (later I'm going to use a SED1352 I think) > and also > other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals. > > I think I can get away with the 3.3V logic levels being able to > trigger the > logic 0 and 1 thresholds of the 5V system so long as I use the ADSP > to drive > into the 5V peripheral. > > It's the opposite direction though? 5V -> 3V? Is it best to use a > FET > transistor level shifter? > > 5V_|\|_____|\|___|-----|___ > |/| |/| |_____| | > | > | > ------- > ^ | > | | > 5V system--- ------ 3V system > > One signal diode and one shottky diode giving a total voltage drop > of about > 2V? > > Does anyone recommend a better method or maybe a level converter > chip/driver > that I can buffer the output of the DSP data/address bus with? > Thanks > > Pete > _____________________________________ > Note: If you do a simple "reply" with your email client, only the > author of this message will receive your answer. You need to do a > "reply all" if you want your answer to be distributed to the entire > group. > > _____________________________________ > About this discussion group: > > To Join: Send an email to > > To Post: Send an email to > > To Leave: Send an email to > > Archives: http://www.egroups.com/group/adsp > > Other Groups: http://www.dsprelated.com > |
Reply by ●January 31, 20012001-01-31
Here are some replies I've had. I've collated them here on the
list for an aid to others when browsing the archives in the future. I hope this is O.K. Thanks to all Regards Pete *** QUOTE from Al Clark ********** Do not drive 5V logic into a 2189m! The 3.3V output will be fine for driving the display. Often with LCDs, you don't really need to read. If this is the case, you are fine. The bus with maximum wait states will be too fast for a LCD display. This means you should either use the PF & Flag Lines (I have done this) or write to a 74xx device. If you need to support both read and write use 74 logic (powered by 3.3V that is 5V fault tolerant). The 74VHC family (except the 74VHC245) and the LV families will work. You use the PF lines as outputs. They are the D0-D7 lines. FL are E, R/W etc. You can use a 74VHC574 or 74VHC273 for the data bus method. The advantage of the 273 is that you can tie the G lpin to reset to clear the FFs. *** QUOTE from Sigurd ************ The 74ALVT_ family from Phillis Semiconductors should do the job The 74ALVT16244 is a high-performance BiCMOS product designed for VCC operation at 2.5V or 3.3V with I/O compatibility up to 5V. You should also look up the SN74LVCC4245A from Ti. This 8-bit (octal) noninverting bus transceiver uses two separate power-supply rails. The A port, VCCA, is dedicated to accept a 5-V supply level, and the configurable B port, which is designed to track VCCB, accepts voltages from 3 V to 5 V. This allows for translation from a 3.3-V to a 5-V environment and vice versa. The SN74LVCC4245A is designed for asynchronous communication between data buses. The device transmits data from the A bus to the B bus or from the B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE\) input can be used to disable the device so the buses are effectively isolated. The SN74LVCC4245A is characterized for operation from -40C to 85C. |
Reply by ●January 31, 20012001-01-31
On Tue, 30 Jan 2001 09:51:26 +0200, wrote: > Has anybody taken any special precautions when attaching 5V logic devices to > the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any > ADSP design) Since this problem isn't restricted to ADI DSP's, I'd suggest posting your question on a more general electronics forum, such as the comp.arch.embedded newsgroup, or one of the sci.electronics.* newsgroups. I know the problem has come up in the design I work on and we use 3v-tolerant logic in one direction and level shifters in the other, but I don't know the details as I mainly deal with the software. Much of our 5v logic is actually on a separate power supply and we both optically couple to it and use differential transceivers for SPORT connections, making the system very noise- and ESD-immune. This is critical in a factory environment where a customer might accidentally plug one's product into hostile electrical gear. |
Reply by ●January 31, 20012001-01-31
>Has anybody taken any special precautions when attaching 5V logic devices >to >the 3.3V ADSP-2189X devices? (Especially the EZKIT LITE but related to any >ADSP design) We use Fairchild LVX4245 translator devices between an ADSP-2187L and our 5V sensor. > >I've got an LCD (see newbie question earlier) which has a 5V interface to a >Toshiba T6963 controller (later I'm going to use a SED1352 I think) and >also >other 5V devices. Thus I have a mixture of 5V and 3.3V peripherals. > >I think I can get away with the 3.3V logic levels being able to trigger the >logic 0 and 1 thresholds of the 5V system so long as I use the ADSP to >drive >into the 5V peripheral. > >It's the opposite direction though? 5V -> 3V? Is it best to use a FET >transistor level shifter? > >5V_|\|_____|\|___|-----|___ > |/| |/| |_____| | > | > | > ------- > ^ | > | | > 5V system--- ------ 3V system > >One signal diode and one shottky diode giving a total voltage drop of about >2V? ADI suggest a similar circuit in one of their app. notes. I forget which one. Leon -- Leon Heller, G1HSM Tel: (work): +44 1327 357824 (home): +44 1327 359058 Email: My web page: http://www.geocities.com/leon_heller IRISYS Ltd: http://www.irisys.co.uk _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. |