FT121 Datasheet, PDF (14/46 Pages) Future Technology Devices International Ltd. – FT121 ENHANCED USB DEVICE CONTROLLER WITH SPI SLAVE IC Datasheet Version 1.2

Document No.: FT_000648
FT121 ENHANCED USB DEVICE CONTROLLER WITH SPI SLAVE IC
Datasheet Version 1.2
5 Endpoint Buffer Management
Clearance No.: FTDI# 312
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
Endpoint
Number (EP) 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.
EP2 Endpoint Endpoint
Configuration
Mode
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
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