pins of i.MX6ULL have a setting called "Drive Strength". For example:
Drive Strength Field
Select one out of next values for pad: ENET1_TX_CLK
000 DSE_0_output_driver_disabled_ — output driver disabled;
001 DSE_1_R0_260_Ohm___3_3V__150_Ohm_1_8V__240_Ohm_for_DDR_ — R0(260 Ohm @ 3.3V, 150 Ohm@1.8V, 240 Ohm for DDR)
010 DSE_2_R0_2 — R0/2
011 DSE_3_R0_3 — R0/3
100 DSE_4_R0_4 — R0/4
101 DSE_5_R0_5 — R0/5
110 DSE_6_R0_6 — R0/6
111 DSE_7_R0_7 — R0/7
Could you, please, explain what precisely does this setting mean? What impedance is referred to in this definition (what does it come from / where would it be located)? - Is this a current limit of output driver working as a current source in saturation?
- Is this physical resistance connected in series after a voltage source? (In other words, is this equivalent to series terminating resistance inside the chip?)
- Or, something else?
Could you present a precise and complete equivalent electric circuit of the output with this setting?
the description in RM is NOT precise. I can tell at least three interpretations, all matching the description, but with completely different physical effects.
Can you, please, give a precise answer in context of Fig. 28-6 (IMX6ULLRM, Rev. 1, 11/2017, p. 1353)?
This field is internally used to adjust the PAD drive capability internally. The description in RM is very clear:
IO voltage = 3.3V : R0 = 260 Ohm
IO voltage = 1.8V : R0 = 150 Ohm
Using DDR mode : R0 = 240 Ohm
Then we know how much resistance is connected to this PAD.
Hope these information is helpful for you.
Have a nice day!