Document No.: FT_000061
FT2232H DUAL HIGH SPEED USB TO MULTIPURPOSE UART/FIFO IC
Version 2.21
Clearance No.: FTDI#77
4.12 Send Immediate / Wake Up (SIWU#)
The SIWU# function is available in the FIFO modes and in bitbang mode.
The Send Immediate portion is used to flush data from the chip back to the PC. This can be used to get
short packets of data back to the PC without waiting for the latency timer to expire.
This mechanism should only be used when you have stopped sending data to the chip to avoid overrun.
The data transfer is flagged to the USB host by the falling edge of the signal.
CLKOUT
WR#
D7-D0
SIWU#
Figure 4.23: Using SIWU#
When the pin is being used for a Wake Up function to wake up a sleeping PC a 20ms negative pulse on
this pin is required. When the pin is being used to flush the buffer (Send Immediate), a 250ns negative
pulse on this pin is required.
Notes
1. When using remote wake-up, ensure the resistors are pulled-up in suspend. Also ensure peripheral
designs do not allow any current sink paths that may partially power the peripheral.
2. If remote wake-up is enabled, a peripheral is allowed to draw up to 2.5mA in suspend. If remote
wake-up is disabled, the peripheral must draw no more than 500uA in suspend.
3. If a Pull-down is enabled, the FT2232H will not wake up from suspend.
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