I am trying to implement the SDO readback using two Eval boards. I have a Board 0 connected to the device running an in-house SPI software via the SPI lines on P3. I then I have a cable going from Board 0 P2 going to Board 1 P1. This way, both boards are sharing the same SPI lines. (Board 1 has address one by connected P10 P4 to P6).
I was trying to understand the readback errata as I will be reading data from the BFICs occasionally. I have found something curious in the setup I have. After writing to the 0A scratchpad of Board 1 and trying to read back the data, I do not get any data unless Board 0 also has SDO activated. The data stream looks something like this (I am always sending 48 bits, with a CS_N toggle after the first 24 bits, with first 24 addressed to board 0 and second 24 addressed to board 1). When CS_N is 'toggled' it goes from low to high, and stays high for about 50ns between writes.
000018 (CS_N toggle) 200018
000a00 (CS_N toggle) 200a33
000a00 (CS_N toggle) a00a44
Here, I get back 0x33. However, if I tell Board 0 0x00000 at the beginning, I don't get back 0x33 (line stays high).
This behavior is not at all what is described in the datasheet or the errata. I realize that this error could be for always writing to both chips, but I was curious to know if this behavior has been witnessed before with the eval boards.
