MPC5777C DSPI SCK vs. MPC5674F

[ricardofranca]

Hello,

I am replacing an MPC5674F (264MHz) with an MPC5777C (300MHz) in a project and I am a bit confused when trying to compute DSPI SCK for the new MCU.

- It seems DSPI SCK for the MPC5777C must be at most 30MHz and DSPI_CLK must be at most 100MHz. I did not quite understand what are these upper bounds for MPC5674F... does "t_SYS" means the same in both datasheets? The MPC5777C datasheet describes t_SYS as the period of DSPI_CLK, being at least 10ns/100MHz, but I could not understand the meaning of t_SYS in the MPC5674F datasheet. Is t_SYS the inverse of f_SYS (i.e. 1/264MHz) or the inverse of the peripheral clock (1/132MHz)?

- Why did the DSPI had such a significant maximum SCK decrease from the 5674F to the 5777C?

- Shall I use PER_CLK at 100MHz or lower if I intend to use DSPI?

- Is there any combination of clocks and multipliers for me to have DSPI SCK at 30MHz with core clock at 300MHz?

Thanks,

Ricardo

[davidtosenovjan]

MPC5674F:
tSCK = 1/fperiph
fperiph=fplatf

If SIU_SYSDIV[IPCLKDIV] = 0 (Enhanced mode): fcore=fsys, fplatf=fsys/2=fetpu
If SIU_SYSDIV[IPCLKDIV] = 1 (Full mode): fcore=fsys=fetpu, fplatf=fsys/2
If SIU_SYSDIV[IPCLKDIV] = 3 (Legacy): fcore=fsys=fplatf=fetpu

MPC5777C:

It can also be limited by used pad types, both devices are based on different nm technology.

[ricardofranca]

Hello David,

I did not understand the references to eTPU - for the moment, I am staying away from it and I could not see any relationship between it and the DSPI clocks. From the MPC5777C datasheet table 44

It seems that maximum frequency of DSPI would be 30MHz. Also in this table, note 6 states that "tSYS is the period of DSPI_CLKn clock, the input clock to the DSPI module. Maximum frequency is 100 MHz (min tSYS = 10 ns). " Thus, even if PER_CLK can reach 150MHz, it seems to me that I am bound to 100MHz if I use DSPI. Is that right?

[davidtosenovjan]

On MPC5777C fetpu only relates that in the fastest option is fperiph*2

Maximum DSPI frequencies are explicitly mentioned below:

100MHz is a limit, if you use clock calculator (AN12176), it is checking this parameter: