FT120T-R Datasheet, PDF (11/40 Pages) Future Technology Devices International Ltd. – USB Device Controller with Parallel Bus IC

Document No.: FT_000646
FT120 USB DEVICE CONTROLLER WITH PARALLEL BUS IC
Datasheet Version 1.2
5 Endpoint Buffer Management
Clearance No.: FTDI# 291
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
0
0
OUT
1
IN
1
2
OUT
3
IN
Table 5-1 Endpoint configuration for EP0 and EP1
Transfer Type
Control
Control
Bulk/Interrupt
Bulk/Interrupt
Max Packet Size
16
16
16
16
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
Endpoint
Configuration
Mode (EP2)
Index (EPI)
Endpoint
Direction
0
4
(default)
5
OUT
IN
1
4
OUT
2
5
IN
3
4
OUT
5
IN
Table 5-2 Endpoint configuration for EP2
Transfer Type
Bulk/Interrupt
Bulk/Interrupt
Isochronous
Isochronous
Isochronous
Isochronous
Max Packet Size
64
64
128
128
64
64
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.
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