SAM4CM_14 Datasheet, PDF (1094/1177 Pages) ATMEL Corporation – Atmel | SMART ARM-based Flash MCU

46.4.3.1 Maximum SPI Frequency
The formulas that follow give maximum SPI frequency in Master write and read modes and in Slave read and write
modes.
Master Write Mode
The SPI is only sending data to a slave device such as an LCD, for example. The limit is given by SPI₂ (or SPI₅)
timing. Since it gives a maximum frequency above the maximum pad speed (see Section 46.4.2 “I/O AC
Characteristics”), the max SPI frequency is the one from the pad.
Master Read Mode
f_SPCKMax = -_S---_P----_I--₀---₍--_o----_r--_S----_P-1---_I--₃---₎---₊-----_t--_v---_a--_l--_i--_d-
t_valid is the slave time response to output data after detecting an SPCK edge. For Atmel SPI DataFlash
(AT45DB642D), t_valid (or T_v) is 12 ns Max.
In the formula above, F_SPCKMax = 40 MHz @ VDDIO = 3.3V.
Slave Read Mode
In slave mode, SPCK is the input clock for the SPI. The max SPCK frequency is given by setup and hold timings
SPI₇/SPI₈(or SPI₁₀/SPI₁₁). Since this gives a frequency well above the pad limit, the limit in slave read mode is
given by SPCK pad.
Slave Write Mode
f_SPCKMax = -2---_x---₍--_S----_P----_I--₆---_m----_a---_x--₍---_o---_r---_S--1-_P----_I--₉---_m----_a---_x--₎----₊-----_t-_s---_e--_t--_u---_p---₎
t_setup is the setup time from the master before sampling data.
1094
SAM4CM Series [DATASHEET]
Atmel-11203C-ATARM-SAM4CM32-SAM4CM16-SAM4CM8-Datasheet_06-Oct-14