Figure 54. An Example Of A Ddr Command In Quad Mode - ST STM32F423 Reference Manual

Quad-SPI interface (QUADSPI)
SDR mode
By default, the DDRM bit (QUADSPI_CCR[31]) is 0 and the QUADSPI operates in single
data rate (SDR) mode.
In SDR mode, when the QUADSPI is driving the IO0/SO, IO1, IO2, IO3 signals, these
signals transition only with the falling edge of CLK.
When receiving data in SDR mode, the QUADSPI assumes that the Flash memories also
send the data using CLK's falling edge. By default (when SSHIFT = 0), the signals are
sampled using the following (rising) edge of CLK.
DDR mode
When the DDRM bit (QUADSPI_CCR[31]) is set to 1, the QUADSPI operates in double data
rate (DDR) mode.
In DDR mode, when the QUADSPI is driving the IO0/SO, IO1, IO2, IO3 signals in the
address/alternate-byte/data phases, a bit is sent on each of the falling and rising edges of
CLK.
The instruction phase is not affected by DDRM. The instruction is always sent using CLK's
falling edge.
When receiving data in DDR mode, the QUADSPI assumes that the Flash memories also
send the data using both rising and falling CLK edges. When DDRM = 1, firmware must
clear SSHIFT bit (bit 4 of QUADSPI_CR). Thus, the signals are sampled one half of a CLK
cycle later (on the following, opposite edge).
Dual-flash mode
When the DFM bit (bit 6 of QUADSPI_CR) is 1, the QUADSPI is in dual-flash mode, where
two external quad SPI Flash memories (FLASH 1 and FLASH 2) are used in order to
send/receive 8 bits (or 16 bits in DDR mode) every cycle, effectively doubling the throughput
as well as the capacity.
Each of the Flash memories use the same CLK and optionally the same nCS signals, but
each have separate IO0, IO1, IO2, and IO3 signals.
Dual-flash mode can be used in conjunction with single-bit, dual-bit, and quad-bit modes, as
well as with either SDR or DDR mode.
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Figure 54. An example of a DDR command in quad mode

RM0430 Rev 8
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