01-08-2019, 08:36 PM
(01-07-2019, 05:51 PM)t4_4t Wrote: Regulator-1.8v
http://www.unisonic.com.tw/datasheet/UT7500.pdf
*Note)
Parts used for "ROCK 64 STEREO AUDIO DAC add-on board" are …
The terminating resistor is "62 Ω".
The manufacturer of the regulator(1.8v) is unknown.
There is no LED display function of "EtherNet".
Isn't that they have used the 1.8V regulator output as they needed it for other means on the shield? Because I think otherwise they could have used the 3.3V VCC available on pin 1 of P5+, which is already regulated, so that you could omit from your scheme the regulator and its two electrolytic caps. Indeed, without knowing exactly the impedance of the RX/TX pins (I couldn't find the value in the RK docs, but I didn't look for it seriously TBH), one could use an equation and calculate the needed resistor value to obtain the same voltage drop on the pins, but having 3.3V as VCC.
SparkFun has a nice article on pull-up/down resistors
The other thing I've noticed in your schema is that the central transformer pin is hooked to VCC and to the capacitor. Indeed, I have left that end dangling on my schema, although I was suspicious about it.
I think it may be useful to add this RockChip wiki page the the Pine64's Rock64 Wiki site. There I've found the schema of a reference design, for instance. Also, on the Rock64 P5+ bus schema pin 21 is reported wrongly as GPIO2_D1 (Ethernet Speed) (and I did the same error in my schema), which is not correct as GPIO2_D1 is PHY's Ethernet Data LED. PHY's Ethernet Speed is GPIO0_D6, which I think is not available as it is used for SDMMC0_PWREN (i.e. the MMC) and not present on the P2 /P5+ connectors.
I wish Rock64 would have a proper/better documentation. IMHO is its weakest point and probably the main reason it is not as widespread as it could.
