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Interfacing 5V dual-ports with both 5V and 3.3V processors

Last Updated: October 11, 2011

- Can I power the 5V dual-port with a 3.3V supply (accepting a reduction in speed)?
- I need to interface the dual-port to 5V parts and to 3.3V parts. Is this going to work safely?
- If the two processors attached to the dual-port have different I/O standards (for example, one processor is TTL and one is CMOS), can I still use your dual-port?


Our 5V dual-ports are guaranteed only to operate with the AC timing characteristics in the datasheet if the power supply to the dual-port is 5V +/- 10% (which means between 4.5V and 5.5V).  Our 3.3V dual-ports are guaranteed to work at 3.3V +/- 10% (which means 3.0V to 3.6V).  It would not be a good idea to power a 5V dual-port with only a 3.3V supply.  If there are constraints with your board which restrict the number of power planes, please note that many of our dual-ports come in both 5V and 3.3V options.  For example, the CY7C028 is a 1M x 16 5V asynchronous dual-port.  The CY7C028V is a 1M x 16 3.3V asynchronous dual-port.  Most of the features remain the same between the two devices.

If you are using the dual-port with two different I/O standards, for example if one port is 5V TTL and the other is 3.3V LVTTL, we can only guarantee that this device will have full functionality every single time if used in stated operating conditions.  As an example, please compare the CY7C028 and CY7C028V electrical characteristics:






2.4V min.

2.4V min.


0.4V max.

0.4V max.


2.2V min.

2.2V min.


0.8V max.

0.8V max.

As the table above shows, the requirements for our 3.3V dual-port are same as the equivalent 5.0V dual-port.  If you have a 5V processor on one side and a 3.3V processor on the other, you just need to ensure that the outputs on both the processors meet the input requirements of the dual-port and that the output specifications of our dual-port meet the input requirements of both the processors.

Most of our standard family of synchronous and asynchronous dual-ports are both CMOS and TTL compliant.  It is possible to have one port CMOS and one port TTL.  Both ports do not have to have the same I/O standard.  Most important is that the I/Os meet the above electrical characteristics.

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