FT121Q-R datasheet(31/46 Pages) FTDI

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Document No.: FT_000648

FT121 ENHANCED USB DEVICE CONTROLLER WITH SPI SLAVE IC

Datasheet Version 1.2

Clearance No.: FTDI#

312

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 6.18 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 6.19 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

FT121 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 FT121 by driving the SUSPEND pin to LOW, followed by the Send

Resume command.

6.4.3 Set 3-wire Mode

Command

: E8h

Data

: None

This command is used to enable the 3-wire SPI mode. Once enabled, the MOSI pin will become bi-

directional line and the MISO pin is not functional. Both SPI master and slave will drive data on the MOSI

line.

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