NXP Semiconductors K22F series, Reference Manual, Page: 1100 / 1407

USBx_TOKEN field descriptions
Field Description
7–4
TOKENPID
Contains the token type executed by the USB module.
0001 OUT Token. USB Module performs an OUT (TX) transaction.
1001 IN Token. USB Module performs an In (RX) transaction.
1101 SETUP Token. USB Module performs a SETUP (TX) transaction
TOKENENDPT Holds the Endpoint address for the token command. The four bit value written must be a valid endpoint.
43.4.20 SOF Threshold register (USBx_SOFTHLD)
The SOF Threshold Register is used only in Host mode (HOSTMODEEN=1). When in
Host mode, the 14-bit SOF counter counts the interval between SOF frames. The SOF
must be transmitted every 1ms so therefore the SOF counter is loaded with a value of
12000. When the SOF counter reaches zero, a Start Of Frame (SOF) token is transmitted.
The SOF threshold register is used to program the number of USB byte times before the
SOF to stop initiating token packet transactions. This register must be set to a value that
ensures that other packets are not actively being transmitted when the SOF time counts to
zero. When the SOF counter reaches the threshold value, no more tokens are transmitted
until after the SOF has been transmitted.
The value programmed into the threshold register must reserve enough time to ensure the
worst case transaction completes. In general the worst case transaction is an IN token
followed by a data packet from the peripheral device followed by the response from the
host. The actual time required is a function of the maximum packet size on the bus.
Typical values for the SOF threshold are:
• 64-byte packets=74;
• 32-byte packets=42;
• 16-byte packets=26;
• 8-byte packets=18.
Address: 4007_2000h base + ACh offset = 4007_20ACh
Bit 7 6 5 4 3 2 1 0
Read
CNT
Write
Reset
0 0 0 0 0 0 0 0
USBx_SOFTHLD field descriptions
Field Description
CNT Represents the SOF count threshold in byte times.
Memory map/Register definitions
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1100 NXP Semiconductors