Question about electronic terms (SMII/SS-SMII, TX, RX)

[HOSSEINGHODS]

Hi
Following sentences are some parts of a datasheet, please take a look at them and tell the difference between the marked terms.

• In SMII/SS-SMII, TXD1 is not used and should be tied either high or low.
• In SMII/SS-SMII, RXD1is not used and they are driven low.
• RMII mode;no switch controller is connected; and TX_EN[7:0] is pulled down.
• 'Pd' stand for internal pull down (75K ohm)

Thanks in advance.

 

[mjuneja]

Hi
Following sentences are some parts of a datasheet, please take a look at them and tell the difference between the marked terms.

• In SMII/SS-SMII, TXD1 is not used and should be tied either high or low.
• In SMII/SS-SMII, RXD1is not used and they are driven low.
• RMII mode;no switch controller is connected; and TX_EN[7:0] is pulled down.
• 'Pd' stand for internal pull down (75K ohm)

Thanks in advance.

Tied high means connected to Vcc using some current limiting resistor.

Tied low/driven low/pulled down/internal pull down means connected to gnd again using current limiting resistor.

 

[HOSSEINGHODS]

Thanks, some other questions;

1. consider a pin which is internally pulled up (with an internal 75 K ohm resistor), is it necessary to pull this pin up externally? I have seen people doing this!
2. what does keep logic low level mean?

 

[mjuneja]

1. I think adding an external pull up resistor will leads to a strong pull up for that particular pin.

2. "keep logic low" --> connecting the specific pin to logic '0' voltage or pulled down.