Reply by Michael Karas●September 24, 20102010-09-24
In article <i7g9ql$63n$1@news.eternal-september.org>,
hamilton@nothere.com says...
>
> 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.com
>
> I 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
Adding a comment too. The main area that you can get into problems here
in transmitting the correct and workable logic levels between a 3.3V MCU
and some 5V memory or peripheral part is in the sending of a logic high
("1") level from the 3.3V part to the 5V part. This is particularly
problematic for the 5V parts that advertise themselves as being "CMOS"
compatible logic levels. For parts that have "TTL" logic levels with a
2.4V VIH then it is easy for the 3.3V output of the MCU to drive the
high level for the device and in this case you have a good situation.
If you happen to be using an MCU device that has I/O pins that work like
those on bog-standard 8051 type parts this 3.3V high to 5V high issue
can easily be mitigated simply by adding pullup resistors to 5V on the
signal lines in question. (There is a speed consideration that needs to
be taken into account here in that a resistive pullup will have an
extended rise time). On the 8051 style of part the output pin does not
operate in push-pull mode and so the pullup it able to get the MCU
output to pull all the way to 5V and overcome the high level drive
problem.
I did not look specifically at what type of I/Os your MCU has but the
simple fact that it specifies 5V tolerant pins means that port pins as
inputs can take this higher voltage. If you have the 8051 type
bidirectional type I/Os then pullups on the outputs are your solution.
If you have I/Os that only operate in push-pull mode, which means that
as outputs they would only drive high out of the MCU at a maximum of the
3.3V supply rail then you have only one other choice and that is to add
the pullup resistors and operate the I/O pins as "open drain" where you
only drive them out as lows ("0") and turn the pin back around as an
input for driving "1"s and let the pullups to 5V give you your high
level.
--
Michael Karas
Carousel Design Solutions
http://www.carousel-design.com
Reply by -jg●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
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 larwe●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 3V
Besides 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 hamilton●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.com
I 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 abrous●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 =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 linnix●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 =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
Reply by Rich Webb●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 abrous●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.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 Ulf Samuelsson●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.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