FT121Q-R FTDI, FT121Q-R Datasheet - Page 14

• Manufacturer Part Number: FT121Q-R
• Description: USB Interface IC USB CONTROLLER W/SPI SLAVE IC
• Manufacturer: FTDI

Specifications of FT121Q-R

• Rohs: yes
• Product: USB 2.0
• Interface Type: SPI, USB
• Operating Supply Voltage: 4 V to 5.5 V
• Operating Supply Current: 3.9 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: QFN-16
• Minimum Operating Temperature: - 40 C

As the primary endpoint, EP2 is suitable for transmitting or receiving relatively large data. To improve the
data throughput, EP2 is implemented with double buffereing. This allows the concurrent operation
between USB bus access and MCU local bus access. For example, for EP2 IN endpoint (EPI5), the USB
host can read data from FT121 Buffer 0 while the local MCU is writing to Buffer 1 at the same time. The
USB host can subsequently read from FT121 Buffer 1 without waiting for it to be filled. Buffer switching is
handled automatically by FT121.
5.2 Endpoint Buffer Management in Enhanced Mode
In enhanced mode the FT121 supports a dedicated 1kB buffer for IN packets and a dedicated 1kB buffer
for OUT packets. The OUT/IN buffer can be allocated to any endpoint with the same direction, up to a
maximum of 504 bytes double buffered (1008 bytes in total) to one endpoint. 504 is the maximum byte
count as there are 1024 bytes in total per OUT/IN Buffer and 8 bytes for IN and OUT packets on control
endpoint 0 must always be reserved. Control, interrupt and bulk endpoints can have a maximum packet
size of 64 bytes and only isochronous endpoints can be allocated more than 64 bytes.
Isochronous modes can have larger buffer sizes as USB packets can be larger than 64 bytes for
isochronous transfer. Isochronous buffers are managed in the same way as bulk, interrupt and control
buffers – i.e. a buffer is for one USB packet only and will not span more than one USB packet.
An example of buffer configurations follows, where Configuration 1 and 2 have larger isochronous buffers.
Table 5-3 Example buffer configuration
Configuration 0
EP
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
Copyright © 2012 Future Technology Devices International Limited
Buffer
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1 (ISO)
1 (ISO)
FT121 ENHANCED USB DEVICE CONTROLLER WITH SPI SLAVE IC
(ISO)
(ISO)
Configuration 1
EP
7
7
6
6
2
2
0
0
Buffer
1
0
1
0
1
0
1
0
1
0
5 (ISO)
5 (ISO)
Configuration 2
EP
0
0
Buffer
1
0
1
0
Document No.: FT_000648
Clearance No.: FTDI#
Datasheet Version 1.0
312
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