Internal DC DC converter, Pin capabilities and USB question.

Technical discussions around xCORE processors (e.g. xcore-200 & xcore.ai).
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Sciencefiction68
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Internal DC DC converter, Pin capabilities and USB question.

Post by Sciencefiction68 »

Hi. Im trying to design a custom board using XS1-U10A-128-FB217-C10 . Hope you will help me with my struggle . Thanks in advance.

Q1. Do i have to use internal DC DC converter ? I have both 5v and 3.3V regulators on board. What are the disadvantages of not using internal DC DC con. of device ? Is there any drawbacks on power management system ? Does it affect power consumption? Asleep mode? Or anything at all ? Do i have to connect inductors to sw pins if ill power device via 3.3v supply ?

Q2. This is actually simple one but i got confused so wanted to make clear. Question is about USB_VBUS pin. Datasheet states :
The USB_VBUS pin must be connected to the USB-connector. If the system is not bus-powered, a 2.2uF capacitor to ground should be included on the VBUS pin of the USB-connector.
On the other hand example schematics on the same datasheet doesn't include neither connection vbus pins of connector and device nor 2.2uF cap. I also checked startkit's schematic. They show a connection between vbus pins And 2.2uF cap. I want my board to be powered both by USB and power jack. How should i deal with VBUS ? If im not mistaking VBUS is used both for powering and informing device of USB connectivity. If so shall i use a diode to prevent power from 5V trail back to IC when USB not connected ?

Q3. Can any type of softip blocks (UART ISP LAN ect. ) be created inside ic and connected to any pin of IC ? Or pins must be in some kind of order like next to each other ? Or Can any block created using pins of both tiles or all pins must be on same tile?

Thanks again
Orkhan Aliyev


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segher
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Post by segher »

Q1: The DC-DC converters.

The digital tiles require a 1.0V supply. The analogue tile
needs 1.8V. The two built-in DC-DC converters convert
a 5V or 3.3V supply to the proper voltages.

The I/O also requires a 3.3V supply. You can power the
whole chip from a single 3.3V, or use a separate 5V to feed
the converters (this is more efficient).

You can provide the 1.0V and 1.8V from an external source,
but why?
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Ross
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Post by Ross »

Sciencefiction68 wrote:
Q2. This is actually simple one but i got confused so wanted to make clear. Question is about USB_VBUS pin. Datasheet states :
The USB_VBUS pin must be connected to the USB-connector. If the system is not bus-powered, a 2.2uF capacitor to ground should be included on the VBUS pin of the USB-connector.
On the other hand example schematics on the same datasheet doesn't include neither connection vbus pins of connector and device nor 2.2uF cap. I also checked startkit's schematic. They show a connection between vbus pins And 2.2uF cap. I want my board to be powered both by USB and power jack. How should i deal with VBUS ? If im not mistaking VBUS is used both for powering and informing device of USB connectivity. If so shall i use a diode to prevent power from 5V trail back to IC when USB not connected ?
It is best to wire up vbus (I am told the data sheets are being updated regarding the example schematics).

For USB compliance the pull-ups on the D+/D- lines must be disabled when VBUS is not present - so the chip needs this signal. When the device is bus powered you can get away without it since the device is not powered on unless it is connected to vbus (and therefore the pull-ups are only enabled when vbus is present...)

Regarding diode, yes some sort of OR circuit should be used if you want the device to be either bus OR self (jack) powered. This board has a good circuit using a fet and a diode: http://www.xmos.com/en/products/reference-designs/mfa
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segher
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Post by segher »

Q3: Pins.

All digital I/O pins are electrically similar. On the other hand,
you use pins via ports, and not every pin connects to every
port (or every width port). Look at the port map (e.g. in the
datasheet) to see which pin can be used for which port (or
which width port).

Ports can only be driven directly from the processor on the
same tile. Tile #0 has few digital pins, mostly 1-bit ports;
#1 has many, also wider ports. You will typically run all
USB stuff on #0 and most other stuff on #1; dividing your
design into tasks and placing them is the hardest job,
everything else is a "mere matter of programming" ;-)
Sciencefiction68
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Post by Sciencefiction68 »

Hello and Thanks for your help:) .

Datasheet has many little mistakes. Like one below :
The XS1-U10A-128-FB217 includes two DC-DC buck converters that take input
voltages between 3.3-5V and output the 1.8V and 1.0V circuits required by the
digital core and analogue peripherals. The DC-DC converters should have a 4.7uF
X5R or X7R ceramic capacitor and a 100nF X5R or X7R ceramic capacitor on the
VSUP input pins V6 and W6.
Example schematics and pin map of board shows that V6 and W6 are SW pins. Caps must be connected to V7 and W7. These little things are confusing.
Sciencefiction68
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Post by Sciencefiction68 »

segher wrote:Q3: Pins.

All digital I/O pins are electrically similar. On the other hand,
you use pins via ports, and not every pin connects to every
port (or every width port). Look at the port map (e.g. in the
datasheet) to see which pin can be used for which port (or
which width port).

Ports can only be driven directly from the processor on the
same tile. Tile #0 has few digital pins, mostly 1-bit ports;
#1 has many, also wider ports. You will typically run all
USB stuff on #0 and most other stuff on #1; dividing your
design into tasks and placing them is the hardest job,
everything else is a "mere matter of programming" ;-)
Hi again. Im having trouble reading the pin port map :S

P32A29 Means Bit 29 of 32bit port A ??

or P8B2 Means Bit 2 of 8 bit port B ??

And some pins can be bits of 4 8 16 even 32 bit ports. Kinda interchangeable. Its Fine as long as they are on same tile. But How come some bits of 32 bit port located on X0 while majority of them are on X1?? And same goes for 16bit port?

Additional off-topic question. I liked 3x3 LED grid on startkit and would like to implement it on my design too. I noticed all 9 LEDs are on same port and same tile 0. I want my grid to be on tile 0 too but then it cant be connected to only 1 port. The widest port on tile 0 is 8 bit port and i still need +1. I can use 1 bit port for it. But question is will it make any complications in terms of coding?
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Bianco
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Post by Bianco »

P32A29 Means Bit 29 of 32bit port A ??

or P8B2 Means Bit 2 of 8 bit port B ??
yes
yes
And some pins can be bits of 4 8 16 even 32 bit ports. Kinda interchangeable. Its Fine as long as they are on same tile. But How come some bits of 32 bit port located on X0 while majority of them are on X1?? And same goes for 16bit port?
Be careful here. Each tile has the same port 'coding', so P1A on tile 0 does not connect to the same physical pin as P1A on tile 1. Likewise for the 32-bit width port. Keep in mind that in some packages the 32-bit port is not fully pinned out. So for your dual-tile device you will have two 32-bit ports, both of them may not be fully pinned out, and both of them are named 32A.

In XC you would reference them as follows:

Code: Select all

on tile[0] : port 32b_port_on_tile0 = XS1_PORT_32A;
on tile[1] : port 32b_port_on_tile1 = XS1_PORT_32A;
Sciencefiction68
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Post by Sciencefiction68 »

Understood Thanks :)
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