AT43USB320A_04 ATMEL [ATMEL Corporation], AT43USB320A_04 Datasheet - Page 91

• Manufacturer Part Number: AT43USB320A_04
• Description: Full-speed USB Microcontroller with an Embedded Hub
• Manufacturer: ATMEL [ATMEL Corporation]

Selective Suspend
and Resume
1443E–USB–4/04
The host can selectively suspend and resume a port through the Set Port Feature
(PORT_SUSPEND) and Clear Port Feature (PORT_SUSPEND).
A port enters the suspend state after the microcontroller interprets the suspend request and
sets the appropriate bits of the Hub Port Control Register, HPCON. From this point on he hub
repeater hardware is responsible for proper actions in placing Ports [1:4] in the suspend mode.
For Port 5, the embedded function port, the hardware will stop responding to any normal bus
traffic, but the microcontroller firmware must place all external circuitry associated with the
function in the low-power state.
A po rt e xits from the susp end state wh en th e hu b re ceive s a C lea r Port Featu re
(PORT_SUSPEND) or Set Port Feature (PORT_RESET). If the Clear Port Feature
(PORT_SUSPEND) is directed towards Ports [1:4], the USB hardware drives a "K" down-
stream for at least 20 ms followed by a low speed EOP. It then places the port in the enabled
state. A Clear Port Feature (PORT_SUSPEND) to Port 1 (the embedded function) causes the
firmware to wait 20 ms, take the embedded function out of the suspended state and then
enable the port.
The ports can also exit from the suspended state through a remote wakeup if this feature is
enabled. For Ports [1:4], this means detection of a connect/disconnect or an upstream
directed J to K signaling. Remote wakeup for the embedded function is initiated through an
external interrupt at INT0.
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