LeafLabs Garden » Topic: R3 Schematic - What does DISC & circuitry around USBDP do?

LeafLabs Garden » Topic: R3 Schematic - What does DISC & circuitry around USBDP do? http://forums.leaflabs.com/topic.php?id=95 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:08:59 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php siy on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7105 Mon, 07 Nov 2011 00:15:55 +0000 siy 7105@http://forums.leaflabs.com/ Well, protection across VBUS is lost with this approach, but this is minor drawback, as for me. Not all IC's contain it anyway and VBUS is not connected directly to MCU. As for other upstream termination/protection IC's, there are a number of them (USBUFxx from ST or STF203, for example). I've used STF202 just because it was simpler to buy in local stores and because it is most convenient for single side board routing :) gbulmer on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7104 Sun, 06 Nov 2011 21:55:14 +0000 gbulmer 7104@http://forums.leaflabs.com/ sly - <blockquote>... STF202 USB upstream protection IC and PNP-driver with built-in resistors. Emitter of the transistor is connected to VCC, base to DISC pin and collector to pin 1 of the IC (VBUS). ...</blockquote> Don't you lose the protection across VBUS using that circuit? (It is still better than the normal USB input which has no protection) Did you look at NUF2042XV6? It doesn't contain the 1.5K data-line pull-up, but is otherwise very similar. siy on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7100 Sun, 06 Nov 2011 16:26:23 +0000 siy 7100@http://forums.leaflabs.com/ By the way: if to use some USB upstream termination IC, which has protection at all lines, direct pin connection might be completely safe. x893 on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7099 Sun, 06 Nov 2011 15:44:42 +0000 x893 7099@http://forums.leaflabs.com/ but i see J-Link schematic (on AT91SAM7S chip) and see that thay use simple connect pin to D+ via 1.5K resistor. May be it normal for short line and not accepted for long distane in factory application (joke)? siy on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7098 Sun, 06 Nov 2011 14:40:20 +0000 siy 7098@http://forums.leaflabs.com/ Probably because there is a danger of overvoltage and/or electric discharge. Beside that I see no problems with such an approach (note about bootloader and inversion applies here as well). x893 on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95&page=2#post-7097 Sun, 06 Nov 2011 12:48:54 +0000 x893 7097@http://forums.leaflabs.com/ Why not connect 1.5K resistor directly to pin and set pin to high for USB D+ current ? siy on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-7096 Sun, 06 Nov 2011 12:35:11 +0000 siy 7096@http://forums.leaflabs.com/ Using OC output is a good idea, but it requires inversion of logic in maple bootloader (since current schematic is inverting). ala42 on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-7095 Sun, 06 Nov 2011 11:15:47 +0000 ala42 7095@http://forums.leaflabs.com/ For the USB disconnect at D+ I use a 1k5 pullup to 3.3V and a 470Ohm resistor connected to a open collector CPU output pin to pull it down to disconnect. siy on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-7094 Sat, 05 Nov 2011 21:02:59 +0000 siy 7094@http://forums.leaflabs.com/ I've successfully tried even more simple circuit, which replaces both, USB input network and disconnect circuit with only two components: STF202 USB upstream protection IC and PNP-driver with built-in resistors. Emitter of the transistor is connected to VCC, base to DISC pin and collector to pin 1 of the IC (VBUS). Resulting equivalent circuit is almost exact copy of the original (except it uses single PNP transistor instead of two NPN). I've also tried P-channel MOSFET as switch and resulting circuit also works just fine, but it requires two additional resistors (probably only one is actually necessary - between gate and VCC). gbulmer on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-5769 Wed, 27 Jul 2011 08:44:06 +0000 gbulmer 5769@http://forums.leaflabs.com/ I am trying out a much simpler USB Rup (pull-up resistor) circuit. It uses a single P-Channel MOSFET with a pull-up resistor to hold it off by default. The MOSFET source is tied to 3.3V, and the drain to the USB pull-up resistor. Two components vs six. A significant saving in board area and assembly cost. (I have other changes too, which require a new PCB) I have seen the Maple USB Rup circuitry on boards from ST, ETT, and maybe Olimex. (full disclosure: I am not a member of LeafLabs staff.) poslathian on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-5761 Tue, 26 Jul 2011 14:21:34 +0000 poslathian 5761@http://forums.leaflabs.com/ is that a mosfet part? buffalo960 on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-5713 Fri, 22 Jul 2011 18:45:07 +0000 buffalo960 5713@http://forums.leaflabs.com/ Would 2n2222s be sufficient for this application? poslathian on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-4546 Tue, 10 May 2011 13:58:52 +0000 poslathian 4546@http://forums.leaflabs.com/ nail on the head. gbulmer on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-4496 Thu, 05 May 2011 15:06:41 +0000 gbulmer 4496@http://forums.leaflabs.com/ pagercam - <blockquote>Why not just pull up to USB +5V then??? </blockquote> The host determines what speed the USB device wants to run at by looking at which of the two USB data lines, D+ or D-, is pulled up with the 1.5K resistor. This lets the device say it is a low-speed, 1.2Mbits, or full-speed 12Mbits (High-speed is different). Every time a USB device is plugged in, the host also needs to figure out exactly what type of USB device it is. The process the host goes through to determine that is called 'enumeration'. Once the host knows what speed the USB device is running at, the host and device have a chat so the host knows which device driver to use to communicate with the device. Currently Maple changes its USB device from a USB DFU (which is used by the bootloader when a program is being uploaded to it from the host) to a USB serial the rest of the time. Maple needs to force the USB host to changes its mind about what type of device it is by forcing the host to query its type of USB device when it needs to transition between those two USB devices. It does that by disconnecting the pull-up resistor, so it looks like the Maple has been unplugged, then raising it again to trigger the host going through USB 'enumeration'. 1. The resistor can't just be tied to a voltage, or Maple couldn't force the host to 'enumerate' it. Even if LeafLabs made the Maple be a single USB device, IMHO it is better for Maple to be able to force USB re-enumeration because then folks can more easily make the Maple look like different USB devices. By allowing Maple firmware/software to decide when to activate the pull-up resistor, it can go through a pile of internal stuff, getting ready, which again makes it easier to program the Maple to take on different USB device persona's. The USB 2.0 specification is at <a href="http://www.usb.org/developers/docs/" rel="nofollow">http://www.usb.org/developers/docs/</a> The bundle of documents is currently <a href="http://www.usb.org/developers/docs/usb_20_021411.zip" rel="nofollow">http://www.usb.org/developers/docs/usb_20_021411.zip</a> but it changes name with revisions. usb_20.pdf defines the electrical characteristics of USB in Table 7-7 in section 7.3.2 "Bus Timing/Electrical Characteristics" The maximum (signalling) voltage that can be applied to the USB D+/D- lines is called Voh (V subscript OH). For low-speed and full-speed USB Voh maximum is 3.6V, with a minimum of 2.8V (this is the voltage used for signalling data) The 1.5K +/-5% pull-up resistor is used to signal the speed of the USB device to the host USB controller for low-speed or full-speed. The resistor is attached to USB D+ or D- depending on whether it wants to be treated as low-speed or full-speed. The pull-up resistor is 'terminated' by connecting it to a voltage called Vterm (V subscript TERM), and Vterm's value is minimum 3V maximum 3.6V. (I think there is an engineering change notice in that set of documents which recommends that devices should be able to cope with a voltage of up to 4.1V, but I can't see it now) 2. The pull-up resistor should not be pulled up to 5V. So, if you really wanted to connect the pull-up to 5V USB, you could get a value in the 3V to 3.6V range using a couple of diodes in series which will drop about 0.7V each. (full disclosure: I am not a member of LeafLabs staff) anton on "R3 Schematic - What does DISC & circuitry around USBDP do?" http://forums.leaflabs.com/topic.php?id=95#post-4494 Thu, 05 May 2011 02:55:56 +0000 anton 4494@http://forums.leaflabs.com/ gbulmer, D+ pin can be pulled up to 3.3V <a href="http://www.beyondlogic.org/usbnutshell/usb2.shtml" rel="nofollow">http://www.beyondlogic.org/usbnutshell/usb2.shtml</a>