The MAX II can tolerate 3.3V input, I believe. I read some TTL data sheets but they seem all provide typical VOH(3.1V) and minimal VOH(2.4V) only. The max VOH is usually not provided. Could I drive the CPLD i/o pins directly, with the LSTTL outputs?
I will try to use some LVTTL to interface the CPLD, if LSTTL are not qualified. Thank you.
vax, 9000
OK, since nobody answered this question, I did a small experiment. I tested VOH of three TTL chips, F(airchild)74LS244, EL74LS14, DS8835. Vcc is 5.07V. Without load, the outputs are around 6.2V(strange?), 5.0V and 5.0V. With a
10K pull-down resistor, the outputs are around 3.5V, 3.5V, 3.5V. I used a digital multimeter(means high input resistance).So the answer is no, unless a serial resistor is used, and the input diode (in EPM1270, EPM2210) is enabled.
vax, 9000
Where did you find the 3.3V MAX value ? The data I have gives 4V (DC)-4.5V (10% duty cycle) ? On that basis, you would just need to enable the input diode, and from your numbers, draw < 300uA clamping current.
You WILL need to stick to bipolar output structures, and avoid CMOS which may be dangerous in the long term.
-jg
I think you are right. I didn't read the datasheet carefully. Now I find that the clamping diodes only exist within i/o bank 3, and there is power-up sequence restriction too. Another problem is that I failed to find the allowed clamping diode current.
vax, 9000
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