Need connect ENC28J60 to PIC18F4620 --- Anyone tempted this before?

[LED7]

The ENC28J60 is a 3.3V device and the PIC18F4620 is a 5V device this may mean that there could be some difficulty connecting theses devices together due to the differing logic voltage
Any method doing this please?

Thanks

 

[kchriste]

Exchange the PIC18F4620 for a PIC18LF4620 and run both of them at 3.3V. The LF version has a max clock speed of 10Mhz when running at 3.3V Or look at the ENC28J60 datasheet and you'll see they tell you how to mix the ENC28J60 with a 5V device by using a buffer chip:

 

[blueroomelectronics]

or you can use a 74hct125 as a level shifter.

 

[LED7]

That really helped. Thanks very much! Can you please tell what are the advantages and disadvantages of each method used?

 

[kchriste]

The advantage of running the PIC18F4620 at 5V is that it can be clocked up to 40Mhz as opposed to the PIC18LF4620 which has an upper limit of 10Mhz at 3.3V. The disadvantage of mixing 5V and 3.3v tech is that you need two voltage regulators and the extra level shifter IC(s). The route I would take is to find a 3.3V PIC ( PIC18F45K20, PIC18LF4620, etc) that you can clock at whatever speed you need and eliminate any extra parts required.
You could also look at the PIC18F97J60 and other PICs which have built in ethernet and you won't need the ENC28J60 at all.

 

[sarad]

you can use a pull up resistors

 

[LED7]

hi thanks for your advice. I just want to know the advantagas/disadvantages for the following methods:
- using quad and gate(74ACT125); or
-using quad-3state buffer;or other 5VCMOS chips to provide the lervel shifting
so I can decide which method to use and make a start
I just want to work out how to connect the PIC18F4620 to The ENC28J60 without trying alternatives!.

 

[blueroomelectronics]

Here's a link to a .png of an Ethernet kit I was working on, I've switched to the 18F87J60 for my kit version.
**broken link removed**

 

[LED7]

thanks very much! It can not get any clearer. Appears to be just what i was looking for.

 

[blueroomelectronics]

If you don't mind the hit in speed you can connect the ENC28J60 CLKOUT to the PICs OSC in (and save the crystal) it's 25MHz/4 by default but you can PLL it back to 25