FT122 datasheet(29/47 Pages) FTDI

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Document No.: FT_000647

FT122 ENHANCED USB DEVICE CONTROLLER WITH PARALLEL

BUS

IC Datasheet Version 1.1

Clearance No.: FTDI#

313

6.4.1 Read Current Frame Number

Command

: F5h

Data

: Read One or Two Bytes

Bit

Symbol

Reset

Description

7-0

Frame Number LSB

00h

Frame number for last received SOF, byte 1 (least

significant byte)

Table 6-19 Frame Number LSB Register

Bit

Symbol

Reset

Description

2-0

Frame Number MSB

0b’000

Frame number for last received SOF, byte 2 (Most

significant byte)

7-3

Reserved

0b’00000

Reserved

Table 6-20 Frame Number MSB Register

6.4.2 Send Resume

Command

: F6h

Data

: None

To perform remote-wakeup when suspended, the MCU needs to issue Send Resume command. The

FT122 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 FT122 by drive SUSPEND pin to LOW, followed by Send Resume

command.

6.4.3 Set Buffer Interrupt Mode

Command

: ECh (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 at a read interrupt command. In this case the FT122 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 FT122 therefore needs to know whether to prime at 2 or 4 bytes. The Set Buffer Interrupt Mode

command notifies the FT122 to prime after 4 bytes.

FT122 Datasheet(PDF) 29 Page - Future Technology Devices International Ltd.

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