Hi team，
I'm driving a TFT(1920*720) via UB949 and UB948, and I need read the touch data via i2c of ub949 with BCC . how many bps can be approximated if the host I2C and Remote I2C work on 400kbps？
Hi BRs,
The UB925/6 and UB948/9 use the same FPD-Link protocol (FPD-Link III) so the host/remote bit calculations are the same. However the UB925/6 has a fixed back channel rate of 5Mbps while the UB948/9 can select back channel rates of 5Mbps, 10Mbps, or 20Mbps.
This means that if you are using the back channel rate of 5Mbps, and the remote and host I2C rate is 400 kbit/s then you can approximate a net bit rate of 163.6 kbit/s based on the app note I linked previously.
However if you use select a different back channel rate then the BCCdelay will scale proportionally down as you increase the back channel rate. The BCC frame is 30 bits wide, which can be used in conjunction with the back channel rate to calculate the BCCdelay (to be more conservative you can calculate the BCCdelay with 60bits to account for the possibility of the 8bits of I2C data being put in the second back channel frame due to timing issues). I have included an example of the calculations you would do with the UB948/9 based on the 400 kbits/s remote and host I2C rate:
Equation: 9 bits / ((Host_bit * 9) + (Remote_bit * 9) + FCdelay + BCCdelay
Host_bit = 2.5us (400 kHz)
Remote_bit = 2.5us (400 kHz)
FCdelay = 1us (max)
BCCdelay = 30bits/10Mhz = 3us + 3us (for processing delay) = 6us
Effective rate = 9bits / ((2.5us*9) + (2.5us * 9) + 1us + 6us) = 173.1 kbit/s
The only thing you should have to adjust depending on the back channel rate you need in the UB948/9 is the BCCdelay (I've bolded the number you would adjust). Please let me know if you have any further questions.
Best,
Corinne
