Having made a mistake in my board design, I'd like to figure out whether I can (reasonably easily) get around it and make it work.
As indicated in the subject, I'm using the ADAU1701 with an external EEPROM for self-boot. The circuit is similar to the ADAU1701 mini evaluation board, so I will program the ADAU with a USBi from SigmaStudio.
The mistake I made is that I placed a chip that is driving the RESET line (without jumper or switch to selectively disconnect it). The RESET line (the one that goes to the ADAU1701, labeled AUDIO_RESET in the schematic, shown below) is being held at logical 0. The one that comes from the USBi (labeled AVR_RESET in the schematic), at this point has absolutely no effect --- it is connected to the RESET pin of an AVR microcontroller, with a 10k pullup.
SigmaStudio cannot connect to the board to download the compiled model, or save latest compilation to EEPROM. In either case, it "freezes" and when interrupted it reports it could not connect.
I am supplying power to the board (separately --- a 12V input goes to a 3.3V DC/DC switching regulator). Those 3.3V go to the ADAU1701 and to the EEPROM.
Below are the relevant sections of the schematic --- the connections to the USBi and the related ADAU1701 pins.
Question #1: should it work, with the ADAU1701 RESET line being held to 0 (active) ??Question #2: any suggestions to get around the problem?
Sorry for the problems. There are a few other details to take care of.
The Write Protect is being puled up. This is not a problem during normal operation but it is a problem when you are trying to write to the EEPROM. So you need to pull down the WP pin to allow the EEPROM to be programmed. The connection to the ADAU1701 is there to allow the DSP to pull down the WP line when it writes-back the interface registers when triggered.
What I have done in designs is to place a transistor in the design to pull down the write protect. The base of the pre-biased transistor is connected to the USBi-5V Power pin. So when you plug in the USBi it pulls down the WP pin. No jumper required.
So for right now if you can solder on a jumper to pull it down to ground while you are working on it then remove it when you are done.
Let me know if this works for you.
Thanks Dave for your reply and the tips!
Couple of follow-up questions/comments:
Just to double check that I understand correctly --- what you're suggesting is what the schematic below shows, right? Pin 4 of the USBi connector brings in the +5V, correct? (the transistor can have pretty much any β / hFE --- something as low as 1 still guarantees that the transistor saturates)
Let me take these questions a step at a time.
Have a look at this schematic of the Evaluation board:
Note that all the switch does is ground the WP pin of the EEPROM. The WP pin of the DSP is still tied to the pullup resistor. So all the switch does is to allow the EEPROM to be programmed. It does not defeat the pullup on the WP pin of the DSP so it will selfboot no matter the position of the switch.
The only thing the switch will mess up is if you are doing write-backs of the interface registers to the EEPROM. And actually, as I think about it. It will not mess that up either. The purpose of the WP pin is to make certain the EEPROM is able to be programmed. If S5 is grounded then the EEPROM can be programmed. If S5 is set to the other position then the WP pin will go low during the Write-back to allow the EEPROM to be programmed. So in the end the switch is really only allowing you to program the EEPROM from the USBi. I always leave my eval board in this position.
I almost never program the EEPROM on my eval board. You can always just load in the program directly from SigmaStudio using the Link/Complile/Download command. If there is a program in the EEPROM I would wait a second to let it load in after powering up before trying to write a new program into it. If Selfboot is enabled then the I2C port becomes a master port while it loads in from the EEPROM. I don't find this to be a problem since I normally plug in the power using the USBi and then it takes me usually more than a second before trying to load in a program.
What the Link/Compile/Connect command is for is to let the DSP boot up from the EEPROM. Then if you want to control the program from SigmaStudio you do NOT download, you only connect to it. Then the objects on the screen will send the commands to the DSP for changing the settings etc. Or looking at meters. The program in SigmaStudio MUST be the exact same program that is resident on the EEPROM. Otherwise, the addresses of the DSP objects will probably be different.
Looking at your schematic, I would tack a ground wire to one side of R12 instead of trying to get to the pins on either the DSP or the EEPROM. I don't know what size resistors you used but there should be more room there.
Now as I get older I know it gets more difficult. I invested in a good magnifier headset that makes me look like a total nerd but it really works well! Then I also use tricks like resting my pinky finger down on something when soldering to help steady my hands. It really helps a lot.
So now to your last comments. If you are getting a message about there needing to be development hardware attached, then there is an issue with your connection to the DSP. Do you have the USBi attached in the Hardware Configuration window? Is it set to the proper address? Are you getting a window saying that there was a communication issue? There is nothing special about the eval board. All you need is SCL and SDA connected and the ground.
Thanks so much for your patience with this --- as usual, your replies are very helpful!
Yes, it worked --- I could (barely) solder the jumper, and after that I could download to E2PROM and the Compare option now reports that the E2PROM matches the latest compilation.
I'm still a bit fuzzy about the RESET --- I was convinced that the USBi needed to drive the ADAU's RESET line, but I think as my board is right now, the lines are disconnected, and it still worked. Could you confirm this detail?
Glad you are making progress.
You will need a pull-down resistor on the base of the transistor so that the device will be off when no USBi is connected. You are correct in that all you want to do is use the transistor as a switch. So any general purpose transistor will work.
You should read this old document about the USBi. Most of this is still relevant.
In here is describes in Figure 15 some of the hidden function of the USBi. If you right click on the USBi GUI you get several options. The "Device Power ON/OFF" is where you can shut off the 5V output of the USBi and turn it back on. Can be handy sometimes. It is a way to reset the board with a full powerdown.
Then the next selection, "Device Enable/Disable" is actually the reset line you are talking about. The USBi never uses this reset so that is why it made no difference for you. However, I do suggest connecting it in your design. This way you can remotely reset the DSP from SigmaStudio on your computer. I use it this a lot. I program the EEPROM then I reset the DSP and see if it loads correctly. I don't need to find the reset switch is there is one on the PCB.
Don't be confused with the Rest USB Device, this is the USBi itself and you should never have to do that.
The only thing I do not like about these settings is that you have no idea of the current state of the control. There are no checkmarks on the pull down menu. So the USBi might be holding the DSP in reset and you cannot tell. I think there was a limitation on the hardware.
Look at Figure 24 in the document. It is an example of using the 5V output to control something on a PCB.
Another thing with this APP Note, the schematic shows the pinout of the USBi connector as a 14 pin connector. That is what is on the PCB but we stuff it with a 10-way. So the pin numbers are not correct from the viewpoint of a 10-way connector. So keep that in mind.