interface MAX-II with 5V device

[Altera_Forum]

Can MAX-II series CPLD interface with 5V operated device and operating frequancy is 40MHz? 

e.g. Interface a Microcontroller (operated on 5V and oscillator 40MHz) data bus with 3.3V operated MAX-II CPLD.

[Altera_Forum]

--- Quote Start ---  Can MAX-II series CPLD interface with 5V operated device and operating frequancy is 40MHz? e.g. Interface a Microcontroller (operated on 5V and oscillator 40MHz) data bus with 3.3V operated MAX-II CPLD.  --- Quote End ---  Read the MAX II handbook:  http://www.altera.com/literature/lit-max2.jsp  p73 of the PDF indicates 4.6V absolute maximum voltage for inputs. So no, you cannot interface directly with 5V.  However, you could use a 3.3V powered, 5V tolerant, buffer on signals from the micro to the CPLD (eg., Fairchild and TI TinyLogic devices). The 3.3V signals from the CPLD to the micro will be fine, no buffering required. If you have a bidirectional bus between the CPLD and micro, then use a bus-switch. You power a bus-switch from a diode drop below 5V (giving about 4.3V) and the bus switch will clamp signals to about 1V below that level, i.e., the 5V signals will be clamped to 3.3V (eg., TI, Fairchild, and Pericom).  Cheers, Dave

[Altera_Forum]

As per reference document downloaded from Altera’s site, can be interface 5V signal to 3.3V operated CPLD using pull up and series resistor connected to IO pin and between two IC, but as per calculation, value of these resistors are very low, approx 200 Ohm, if operating frequency of signal is 40MHz. And if 20-25 signals (16 bit Bidirectional bus and control signal) are connected as above mentioned way then current sinking from VCC is very high. So is it feasible to use this configuration in my application? or there is only way to use level shifter in between two ICs.  

 Regards, Pankaj

[Altera_Forum]

--- Quote Start ---  As per reference document downloaded from Altera’s site, can be interface 5V signal to 3.3V operated CPLD using pull up and series resistor connected to IO pin and between two IC, but as per calculation, value of these resistors are very low, approx 200 Ohm, if operating frequency of signal is 40MHz. And if 20-25 signals (16 bit Bidirectional bus and control signal) are connected as above mentioned way then current sinking from VCC is very high. So is it feasible to use this configuration in my application? or there is only way to use level shifter in between two ICs.     --- Quote End ---  This particular scheme relies on the protection diodes in the CPLD I/Os conducting. I would not recommend doing this. A 16-bit bidirectional bus can be easily implemented using a single bus switch. Control signals are unidirectional, so those from 5V can be buffered with a Tinylogic device, and driven to the CPLD. The signals from the CPLD can drive directly to the 5V micro without any buffers.  Cheers, Dave