Grand Central M4 - how to boot directly to app

Please tell us which board you are using.
For CircuitPython issues, ask in the Adafruit CircuitPython forum.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
User avatar
adafruit_support_mike
 
Posts: 67446
Joined: Thu Feb 11, 2010 2:51 pm

Re: Grand Central M4 - how to boot directly to app

Post by adafruit_support_mike »

No, we don’t have any design documents for the LED matrices. We don’t make them, we just get them on the secondary market for companies that make video billboards.

I trust your measurements, but am a little surprised. The pull-up on OE makes sense.. it puts the matrix in a well-defined state when that line isn’t connected to anything. CLK and LATCH are the ones I wouldn’t expect.

What resistance do you see between those pins and the matrix’s 5V terminal?

User avatar
MikeGrobler
 
Posts: 9
Joined: Fri May 07, 2021 6:03 pm

Re: Grand Central M4 - how to boot directly to app

Post by MikeGrobler »

Here are the resistances (Ohms) between 5V and Gnd:
Item to 5V to Gnd
------- -------- -----------
Clk: 10k 12k
OE: 4.65k 6.8k
Latch: 10k 11k
Inputs: 480k 480k

User avatar
adafruit_support_mike
 
Posts: 67446
Joined: Thu Feb 11, 2010 2:51 pm

Re: Grand Central M4 - how to boot directly to app

Post by adafruit_support_mike »

Thank you.

CLK and LATCH definitely look like 10k pull ups. The 480k for most of the inputs is likely to be trickle current through the input protection diodes.

OE is an odd duck though: it looks like a 4.7k-6.8k voltage divider. Those values would scale a 5V supply voltage down to 3V, which is a reasonable thing to do, I guess.

Having established the resistive connections I didn’t think were there, let’s see which ones are causing trouble at boot time. Disconnect CLK, LATCH, and OE from the Grand Central and see how long it takes to boot. Then connect each of those three pins one at a time to see what effect they have individually. Then connect the permutations for two of them and see what results you get.

Locked
Please be positive and constructive with your questions and comments.

Return to “Metro, Metro Express, and Grand Central Boards”