LCD connected to an 3V3 FPGA

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LCD connected to an 3V3 FPGA

Postby MFF » Tue Feb 02, 2010 2:39 pm

Hello

I need to connect an LCD that uses a 5V logic levels(T6963C) bus to a 3V3 Cyclone II

can someone tell me the simplest and safest way to do.

Tanks a lot
MFF
 
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Postby vlado » Tue Feb 16, 2010 5:49 pm

74lvc244 or 74lvc245.
vlado
 
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Postby caoyaliang » Fri Feb 26, 2010 3:11 pm

you may just connect directly! 3.3v is avalable to device with 5v level. 74lvc244 or 74lvc245 do not work well on high freguency logic.
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Postby Thoma HAUC » Fri Feb 26, 2010 7:24 pm

Hi MFF,

As the LCD is a 5V device and the FPGA is 3.3V device, you MUST observe the following condition:

FPGA -> LCD

Volmax(FPGA) <= Vilmax(LCD)
Vohmin(FPGA) >= Vihmin(LCD)

Vilmax(LCD) = VDD - 2.2
Vihmin(LCD) = 0.8V

LCD -> FPGA
You have a latch-up risk in this configuration. To avoid this phenomenon, you should insert a small resistor on all LCD output and on all LCD directional signals.

Rprotect = (Vohmax(LCD) - Vihmax(FPGA)) / Ilatchup(FPGA)

As the LCD (T6963) has a low operating frequency (5.5MHz), Rprotect should be less than 50ohm.

Hope this help.

Thoma
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Postby vlado » Fri Feb 26, 2010 8:21 pm

I'm not sure why we discuss that? Cyclone II is NOT 5V tolerant inputs device. LCD controller needs 5V. So it's outputs will be pulled up to 5V. There is no any doubt, that FPGA will burn, if you connect its inputs to 5V ouputs of LCD controller. There are 3 ways to solve this problem, but using lvc series logic is the best, when signals are more than 8. In fact lvc series is working in systems at 100Mhz, so I don't think, that device, with max. frequency of 2.4 MHz (as Toshiba's LCD controller) will be affected.
So my suggestion is: don't burn your FPGA. Buy a 1$ buffer and be happy.
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Postby Thoma HAUC » Sat Feb 27, 2010 7:39 am

Hi MFF, hi vlado,

You can use the internal clamping diode by using the 3.3V PCI I/O Standard and a serial resistor. This will not blow up the FPGA.

Take a look to this document http://www.altera.com/literature/hb/cyc/cyc_c51011.pdf

Thoma
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