FT121Q-R datasheet(14/46 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

Endpoint Buffer Management

The FT121 has 2 modes of operation for command and memory management: the default mode and the

enhanced mode. The buffer management schemes are different in these two modes. Upon reset the

default mode is functional. The enhanced mode is activated when any of the Set Endpoint Configuration

commands (B0h – BFh) are received.

5.1 Endpoint Buffer Management in Default Mode

In default mode the FT121 has 3 bi-directional endpoints (EP0, EP1 and EP2). EP0 is the control endpoint,

with 16 bytes maximum packet size for both the control OUT and control IN endpoints. EP1 can be used

as either a bulk endpoint or an interrupt endpoint, with 16 bytes maximum packet size for both OUT and

IN endpoints. Table 5.1 shows the endpoint type and maximum packet size for EP0 and EP1.

Endpoint

Number (EP)

Endpoint

Index (EPI)

Endpoint

Direction

Transfer Type

Max Packet Size

OUT

Control

OUT

Bulk/Interrupt

Table 5.1 Endpoint configuration for EP0 and EP1

EP2 is the primary endpoint. It can be configured as either a bulk/interrupt or isochronous endpoint. The

maximum packet size allowed for EP2 depends on the mode of configuration through the Set Mode

command. Table 5.2 shows all the 4 endpoint configuration modes for EP2.

EP2 Endpoint

Configuration

Mode

Endpoint

Index (EPI)

Endpoint

Direction

Transfer Type

Max Packet Size

(default)

OUT

Bulk/Interrupt

OUT

Isochronous

128

Isochronous

128

OUT

Isochronous

Table 5.2 Endpoint configuration for EP2

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