Document No.: FT_000288
FT232H SINGLE CHANNEL HI-SPEED USB TO MULTIPURPOSE UART/FIFO IC
Datasheet Version 1.8
Clearance No.: FTDI #199
4.12 Send Immediate / Wake Up (SIWU#)
The SIWU# pin is available in the FIFO modes and in bit bang mode.
The Send Immediate portion is used to flush data from the chip back to the PC. This can be used to force
short packets of data back to the PC without waiting for the latency timer to expire.
To avoid overrunning, this mechanism should only be used when a process of sending data to the chip
has been stopped.
The data transfer is flagged to the USB host by the falling edge of the SIWU# signal. The USB host will
schedule the data transfer on the next USB packet.
CLKOUT
WR#
D7-D0
SIWU#
Figure 4.25: 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 used to immediately 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 FT232H will not wake up from suspend when using SIWU#
4.In UART mode the RI# pin acts as the wake up pin.
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