Copyright © 2014 Future Technology Devices International Limited

11

Document No.: FT_000646

FT120 USB DEVICE CONTROLLER WITH PARALLEL BUS IC

Datasheet Version 1.2

Clearance No.: FTDI#

291

5

Endpoint Buffer Management

The FT120 has 3 physical endpoints (EP0, EP1 and EP2) or 6 logical endpoints (EPI0-EPI5). EP0 is the

control endpoint, with 16 bytes maximum packet size for both control OUT (EPI0) and control IN (EPI1)

endpoint. EP1 can be used as either a bulk endpoint or an interrupt endpoint, with 16 bytes maximum

packet size for both OUT (EPI2) and IN (EPI3) endpoints. Table 5-1 shows the endpoint type and

maximum packet size for EP0 and EP1.

Endpoint

Number

Endpoint

Index (EPI)

Endpoint

Direction

Transfer Type

Max Packet Size

0

0

1

OUT

IN

Control

Control

16

16

1

2

3

OUT

IN

Bulk/Interrupt

Bulk/Interrupt

16

16

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.

Endpoint

Configuration

Mode (EP2)

Endpoint

Index (EPI)

Endpoint

Direction

Transfer Type

Max Packet Size

0

(default)

4

5

OUT

IN

Bulk/Interrupt

Bulk/Interrupt

64

64

1

4

OUT

Isochronous

128

2

5

IN

Isochronous

128

3

4

5

OUT

IN

Isochronous

Isochronous

64

64

Table 5-2 Endpoint configuration for EP2

As the primary endpoint, EP2 is suitable for transmitting or receiving relatively large data. To improve the

data throughput, a pair of buffers (the ‘ping-pong’ buffer) is implemented for EP2 buffering. This allows

the concurrent operation between USB bus access and MCU or DMA local bus access. For example, for

EP2 IN endpoint (EPI5), the USB host can read data from FT120 ping buffer while the local MCU is writing

to the pong buffer at the same time. The USB host can subsequently read from FT120 pong buffer

without waiting for it to be filled. Buffer switching is handled automatically by FT120.