Cypress SL811HS - Manual (Page 11)

SL811HS
Document 38-08008 Rev. *D Page 11 of 32
Example: To set up SOF for 1 ms interval, SOF counter register 0Eh should be set to E0h.
SOF Counter High/Control Register 2 [Address = 0Fh]. When read, this register returns the value of the SOF counter divided
by 64. The software must use this register to determine the available bandwidth in the current frame before initiating any USB
transfer. In this way, the user is able to avoid babble conditions on the USB. For example, to determine the available bandwidth
left in a frame do the following.
Maximum number of clock ticks in 1 ms time frame is 12000 (1 count per 12 MHz clock period, or approximately 84 ns.) The value
read back in Register 0FH is the (count Ч 64) Ч 84 ns = time remaining in current frame. USB bit time = one 12 MHz period.
Value of register 0FH Available bit times left are between
BBH 12000 bits to 11968 (187 × 64) bits
BAH 11968 bits to 11904 (186 × 64) bits
Note: Any write to the 0Fh register clears the internal frame counter. Write register 0Fh at least once after power up. The internal
frame counter is incremented after every SOF timer tick. The internal frame counter is an 11-bit counter, which is used to track
the frame number. The frame number is incremented after each timer tick. Its contents are transmitted to the slave every milli-
second in a SOF packet.
When writing to this register the bits definition are defined as follows.
Note Any write to Control register 0Fh enables the SL811HS
full features bit. This is an internal bit of the SL811HS that
enables additional features.
The USB-B register set is used when SL811HS full feature bit
is enabled.
Example. To set up host to generate 1 ms SOF time:
The register 0Fh contains the upper 6 bits of the SOF timer.
Register 0Eh contains the lower 8 bits of the SOF timer. The
timer is based on an internal 12 MHz clock and uses a counter,
which counts down to zero from an initial value. To set the timer
for 1 ms time, the register 0Eh is loaded with value E0h and
register 0Fh (bits 0–5) is loaded with 2Eh. To start the timer,
bit 0 of register 05h (Control Register 1) is set to ’1’, which
enables hardware SOF generation. To load both HIGH and
LOW registers with the proper values, the user must follow this
sequence:
1. Write E0h to register 0Eh. This sets the lower byte of the
SOF counter
2. Write AEh to register 0Fh, AEh configures the part for full
speed (no change of polarity) Host with bits 5–0 = 2Eh for
upper portion of SOF counter.
3. Enable bit 0 in register 05h. This enables hardware gener-
ation of SOF.
4. Set the ARM bit at address 00h. This starts the SOF gener-
ation.
Table 16. SOF Counter LOW Address when Written [Address 0Eh]
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
SOF7 SOF6 SOF5 SOF4 SOF3 SOF2 SOF1 SOF0
Table 17. SOF High Counter when Read [Address 0Fh]
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
C13 C12 C11 C10 C9 C8 C7 C6
Table 18. Control Register 2 when Written [Address 0Fh]
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
SL811HS
Master/Slave
selection
SL811HS
D+/D– Data
Polarity Swap
SOF High Counter Register
Bit Position Bit Name Function
7 SL811HS Master/Slave selection Master = 1, Slave = 0.
6 SL811HS D+/D– Data Polarity Swap ’1’ = change polarity (low speed)
’0’ = no change of polarity (full speed).
5-0 SOF High Counter Register Write a value or read it back to SOF High Counter Register.