STMicroelectronics STM32F405 Reference Manual page 1648

Flexible memory controller (FMC)
Bits 23:16 IOHOLD[7:0]: I/O x hold time
Defines the number of HCLK clock cycles during which the address is held (and data for write
access) after the command deassertion (NWE, NOE), for PC Card read or write access to I/O
space on socket x:
Bits 15:8 IOWAIT[7:0]: I/O x wait time
Defines the minimum number of HCLK (+1) clock cycles to assert the command (SMNWE,
SMNOE), for PC Card read or write access to I/O space on socket x. The duration for
command assertion is extended if the wait signal (NWAIT) is active (low) at the end of the
programmed value of HCLK:
Bits 7:0 IOSET[7:0]: I/O x setup time
Defines the number of HCLK (+1) clock cycles to set up the address before the command
assertion (NWE, NOE), for PC Card read or write access to I/O space on socket x:
1648/1731
0000 0000: reserved
0000 0001: 1 HCLK cycle
1111 1111: 255 HCLK cycles
0000 0000: reserved, do not use this value
0000 0001: 2 HCLK cycles (+ wait cycle introduced by deassertion of NWAIT)
1111 1111: 256 HCLK cycles (+ wait cycle introduced by the Card deasserting NWAIT)
0000 0000: 1 HCLK cycle
1111 1111: 256 HCLK cycles
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