Hi guys,
I have an application in which I have to read / write data to an 5V OTP
EPROM (AT27c020) from an MCU. I have done this many times in the past from
5V microcontrollers like ATmega128. Now I want to do the same from a 3V
device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V
EPROMS since they are rare. Also I don't want to use level shifters since
they increase cost and board complexity. As far as I can see both devices
are CMOS TTL compatible so I think that direct interface would be no
problem logic level-wise. Am I correct or I am missing something ?
Thanks in advance,
Angelo
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Posted through http://www.EmbeddedRelated.com
5V EPROM read/write from 3V mcu
Started by ●September 23, 2010
Reply by ●September 23, 20102010-09-23
2010-09-23 19:15, abrous skrev:> Hi guys, > > I have an application in which I have to read / write data to an 5V OTP > EPROM (AT27c020) from an MCU. I have done this many times in the past from > 5V microcontrollers like ATmega128. Now I want to do the same from a 3V > device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V > EPROMS since they are rare. Also I don't want to use level shifters since > they increase cost and board complexity. As far as I can see both devices > are CMOS TTL compatible so I think that direct interface would be no > problem logic level-wise. Am I correct or I am missing something ? > > Thanks in advance, > > Angelo > > > --------------------------------------- > Posted through http://www.EmbeddedRelated.com1) Write to a 3.3V flash. 2) Assert Write Protect. 3) Done Alternative. Use a 5V 32 bit MCU -- Best Regards Ulf Samuelsson These are my own personal opinions, which may (or may not) be shared by my employer Atmel Nordic AB
Reply by ●September 23, 20102010-09-23
>2010-09-23 19:15, abrous skrev: >> Hi guys, >> >> I have an application in which I have to read / write data to an 5V OTP >> EPROM (AT27c020) from an MCU. I have done this many times in the pastfrom>> 5V microcontrollers like ATmega128. Now I want to do the same from a 3V >> device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V >> EPROMS since they are rare. Also I don't want to use level shifterssince>> they increase cost and board complexity. As far as I can see bothdevices>> are CMOS TTL compatible so I think that direct interface would be no >> problem logic level-wise. Am I correct or I am missing something ? >> >> Thanks in advance, >> >> Angelo >> >> >> --------------------------------------- >> Posted through http://www.EmbeddedRelated.com > >1) Write to a 3.3V flash. >2) Assert Write Protect. >3) Done > >Alternative. >Use a 5V 32 bit MCU > >-- >Best Regards >Ulf Samuelsson >These are my own personal opinions, which may (or may not) >be shared by my employer Atmel Nordic AB >I wish it could be so simple. Saving the data to OTP EPROM is a legal requirement for the specific application. Using a Flash is not an option nor any other type of memory. --------------------------------------- Posted through http://www.EmbeddedRelated.com
Reply by ●September 23, 20102010-09-23
On Thu, 23 Sep 2010 12:15:19 -0500, "abrous" <abrous3d@n_o_s_p_a_m.hotmail.com> wrote:>Hi guys, > >I have an application in which I have to read / write data to an 5V OTP >EPROM (AT27c020) from an MCU. I have done this many times in the past from >5V microcontrollers like ATmega128. Now I want to do the same from a 3V >device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V >EPROMS since they are rare. Also I don't want to use level shifters since >they increase cost and board complexity. As far as I can see both devices >are CMOS TTL compatible so I think that direct interface would be no >problem logic level-wise. Am I correct or I am missing something ?Compare the minimum (not typical) guaranteed output voltage for a logic high and the maximum for a logic low for the microcontroller outputs with the minimum guaranteed voltage to read a logic high, and maximum to read a logic low, on the EPROM. Add in the effects of noise on the data line. Compare the maximum output logic high from the EPROM to the maximum allowed for the microcontroller input. Consider noise again. Compare the max low and min high from the EPROM with the min low and max high on the micro. Consider noise again. One or more of these may vary with temperature or power supply voltage, which itself may vary with load and temperature. Many current generation 3.3 V parts can work transparently with 5 V CMOS and TTL. Some may have difficulty at the edges. You'll have to run the numbers from the datasheets to see if your particular combination is okay. -- Rich Webb Norfolk, VA
Reply by ●September 23, 20102010-09-23
On Sep 23, 11:10=A0am, "abrous" <abrous3d@n_o_s_p_a_m.hotmail.com> wrote:> >2010-09-23 19:15, abrous skrev: > >> Hi guys, > > >> I have an application in which I have to read / write data to an 5V OT=P> >> EPROM (AT27c020) from an MCU. I have done this many times in the past > from > >> 5V microcontrollers like ATmega128. Now I want to do the same from a 3=V> >> device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V > >> EPROMS since they are rare. Also I don't want to use level shifters > since > >> they increase cost and board complexity. As far as I can see both > devices > >> are CMOS TTL compatible so I think that direct interface would be no > >> problem logic level-wise. Am I correct or I am missing something ? > > >> Thanks in advance, > > >> Angelo > > >> --------------------------------------- =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0> >> Posted throughhttp://www.EmbeddedRelated.com > > >1) Write to a 3.3V flash. > >2) Assert Write Protect. > >3) Done > > >Alternative. > >Use a 5V 32 bit MCU > > >-- > >Best Regards > >Ulf Samuelsson > >These are my own personal opinions, which may (or may not) > >be shared by my employer Atmel Nordic AB > > I wish it could be so simple. Saving the data to OTP EPROM is a legal > requirement for the specific application. Using a Flash is not an option > nor any other type of memory. =A0 =A0 =A0You can still write to 5V OTP PROM (OTP would not be EraseablePROM) with 5V MCU as suggested. NUC120 is one of the few 5V compatible 32bits, as least according to the spec. http://www.nuvoton.com/hq/enu/ProductAndSales/ProductLines/IndustrialIC/ARM= Microcontroller/ARMCortexTMM0/Documents/NUC120%20Datasheet%20EN%20V1.02.pdf
Reply by ●September 23, 20102010-09-23
>On Sep 23, 11:10=A0am, "abrous" <abrous3d@n_o_s_p_a_m.hotmail.com> >wrote: >> >2010-09-23 19:15, abrous skrev: >> >> Hi guys, >> >> >> I have an application in which I have to read / write data to an 5VOT=>P >> >> EPROM (AT27c020) from an MCU. I have done this many times in thepast>> from >> >> 5V microcontrollers like ATmega128. Now I want to do the same from a3=>V >> >> device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use3V>> >> EPROMS since they are rare. Also I don't want to use level shifters >> since >> >> they increase cost and board complexity. As far as I can see both >> devices >> >> are CMOS TTL compatible so I think that direct interface would be no >> >> problem logic level-wise. Am I correct or I am missing something ? >> >> >> Thanks in advance, >> >> >> Angelo >> >> >> --------------------------------------- =A0 =A0 =A0 =A0 =A0 =A0 =A0=>=A0 >> >> Posted throughhttp://www.EmbeddedRelated.com >> >> >1) Write to a 3.3V flash. >> >2) Assert Write Protect. >> >3) Done >> >> >Alternative. >> >Use a 5V 32 bit MCU >> >> >-- >> >Best Regards >> >Ulf Samuelsson >> >These are my own personal opinions, which may (or may not) >> >be shared by my employer Atmel Nordic AB >> >> I wish it could be so simple. Saving the data to OTP EPROM is a legal >> requirement for the specific application. Using a Flash is not anoption>> nor any other type of memory. =A0 =A0 =A0 > >You can still write to 5V OTP PROM (OTP would not be EraseablePROM) >with 5V MCU as suggested. > >NUC120 is one of the few 5V compatible 32bits, as least according to >the spec. > >http://www.nuvoton.com/hq/enu/ProductAndSales/ProductLines/IndustrialIC/ARM= >Microcontroller/ARMCortexTMM0/Documents/NUC120%20Datasheet%20EN%20V1.02.pdf > >There is a whole application behind this and a lot of software. I cannot switch to a different MCU now. I am not looking for a workaround. I just want the opinion of the more experienced if the direct interface between a 5V EPROM and a 3,3V (5V tolerant) MCU is going to work. --------------------------------------- Posted through http://www.EmbeddedRelated.com
Reply by ●September 23, 20102010-09-23
On 9/23/2010 11:15 AM, abrous wrote:> Hi guys, > > I have an application in which I have to read / write data to an 5V OTP > EPROM (AT27c020) from an MCU. I have done this many times in the past from > 5V microcontrollers like ATmega128. Now I want to do the same from a 3V > device (LM3S9B90). MCU inputs are 5V tolerant. I don't want to use 3V > EPROMS since they are rare. Also I don't want to use level shifters since > they increase cost and board complexity. As far as I can see both devices > are CMOS TTL compatible so I think that direct interface would be no > problem logic level-wise. Am I correct or I am missing something ? > > Thanks in advance, > > Angelo > > > --------------------------------------- > Posted through http://www.EmbeddedRelated.comI would guess that Vcc and Vpp is the correct value for the AT27c020 to be able to write. I don't see a problem with this, but at the limits of Max Vout from the 3V cpu and Min Vin of the 5V EPROM may be a problem. Also include the Temp limits at Max/Min Vout/Vin. I would also guess that you are bit banging the Add/Data lines to the EPROM, so speed should not be a problem either. Have you tried it yet ?? Is the application Temp controlled, in other words, inside an office and not outside in the sun/sow/rain ? good luck hamilton
Reply by ●September 23, 20102010-09-23
On Sep 23, 1:15=A0pm, "abrous" <abrous3d@n_o_s_p_a_m.hotmail.com> wrote:> I have an application in which I have to read / write data to an 5V OTP > EPROM (AT27c020) from an MCU. I have done this many times in the past fro=m> 5V microcontrollers like ATmega128. Now I want to do the same from a 3VBesides what Rich said, also note that with the lower voltage your timing may need to change depending on the capacitance of your bus lines. I have done similar things to what you describe many times, without difficulty. Not specifically to an EPROM though.
Reply by ●September 24, 20102010-09-24
> There is a whole application behind this and a lot of software. I cannot > switch to a different MCU now. I am not looking for a workaround. I just > want the opinion of the more experienced if the direct interface between a > 5V EPROM and a 3,3V (5V tolerant) MCU is going to work. >If your MCU inputs are 5V tolerant, it should work when you use 5V VCC for the EProm. The Eprom should see the input levels as high when Ue > 2.5V, but you can check this in the datasheet of the EProm Best regards Stefan DF9BI
Reply by ●September 24, 20102010-09-24
On Sep 24, 7:15=A0am, "abrous"> I just > want the opinion of the more experienced if the direct interface between =a> 5V EPROM and a 3,3V (5V tolerant) MCU is going to work. >There are some fish-hooks here, and that's around the VccP value, of 6.50V for the AT27c020. Now, you could need 6.5V tolerant IOs and the Vih will also move up. Since the target is usually TTL, and some parts use NMOS drivers, you might need to carefully measure a real part. All up, a tad risky. What you might prefer, is something like a SST37VF020. That has 3V Vcc, and 12V for erase, so is very close to OTP without it ? See http://www.highbeam.com/doc/1G1-55522828.html ["-- 2.7V-3.6V for read -- 12V needed on OE No. pin for program and erase -- Access speed: 70 nanoseconds (ns) and 90 nanoseconds (ns) -- Fast programming and erase -- 10 microseconds/Byte for programming; 100 milliseconds (ms) for chip erase -- Superior reliability with SST's SuperFlash technology -- At least 1,000 cycles endurance and more than 100 years of data retention -- JEDEC standard flash compatible packages/pinouts for ease of use without any board layout changes -- 32-pin PLCC/PDIP/TSOP -jg
