DRV8904-Q1: Maximum daisy chaining length and connections

SJ,

DRV8904-Q1 supports up to 63 devices in series per daisy chain connection. 20x22 module matrix needs several daisy chain

1. Does the driver repeat the shifted out data or just passthrough them?

Yes.

2. (200ns * 16bit) * (20 * 22) is about 710Hz, is this correct way of calculating refresh rate?

DRV8904-Q1 supports up to 63 devices in series per daisy chain connection. According to "Figure 72. Daisy Chain SPI Operation", each command could be longer than 16 bits.

3. what happens to the chain if single module fails in the middle?

It depends the failure mode. If the failure keeps same bit length and the failure is just value error, it can shift out and only that single module gets failure. If the failure create more bits, it may cause whole command failure.

Dear Wang,

Thank you for your prompt response.

Now that reading datasheet with max 63 device in mind I understand how it works.

So max 63 devices command would be:
2*hdr_byte + 63*addr_byte + 63*data_byte = 1024 bit 

It makes sense with reporting feature,

but do you have other driver which simply just shift out and execute final command on SCS?

Please let me know if such process is not possible.

I appreciate your support

Wang5577 said:

TI motor SPI command format is similar as DRV8904-Q1.

If the driver simply just shift out and execute final command, it seems not work. For example: when the 3rd motor driver command pass the 1st motor driver device, what the 1st motor driver should do?

I don't get this.

In typical simple SPI chain, I might send command for 3 devices. perhaps like (where bold is final command executed):

Please correct me if I got something wrong.

SJ,

I think we have to add the header bytes which contain information of the number of devices connected in the chain.