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Application Note
AN_289 FT51A Programming Guide
Version 1.0
Document Reference No.: FT_000962 Clearance No.: FTDI# 483
105
Copyright © 2015 Future Technology Devices International Limited
2.11.5
General Commands
2.11.5.1
Read Current Frame Number
Command
: 0xF5
Data
: Read One or Two Bytes
Bit
Symbol
Reset
Description
7..0
Frame Number LSB
0
Frame number for last received SOF, byte 1 (least
significant byte)
Table 2.133 Frame Number LSB Register
Bit
Symbol
Reset
Description
2..0
Frame Number MSB
0
Frame number for last received SOF, byte 2 (Most
significant byte)
7..3
Reserved
0
Reserved
Table 2.134 Frame Number MSB Register
2.11.5.2
Send Resume
Command
: 0xF6
Data
: None
To perform remote-wakeup when suspended, the CPU needs to issue a Send Resume command.
The USB Full Speed device controller will send an upstream resume signal for a period of 10 ms. If
the clock is not running during suspend, the MCU needs to wakeup FT122USB Full Speed device
controller by drive SUSPEND pin to LOW, followed by Send Resume command.
2.11.5.3
Set Buffer Interrupt Mode
Command
: 0xEC (for Enhanced Mode)
Data
: none
The read or write buffer commands can be interrupted, typically by a read interrupt register or
read last transaction status command, and can be resumed without having to re-issue a read or
write buffer command. When the default command set is in use, a read or write buffer command
can be resumed after 2 bytes have been read with a read interrupt command. In this case the USB
Full Speed device controller design is primed to resume a read or write buffer command if another
command is not issued and a read or write occurs.
For the enhanced command set the read interrupt register command has been extended to read 4
bytes. The USB Full Speed device controller therefore needs to know whether to prime at 2 or 4
bytes. The Set Buffer Interrupt Mode command notifies the USB Full Speed device controller to
prime after 4 bytes.