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Table 4-23. Endpoint Control Register Definitions
EP_CTL_DIS EP_RX_EN EP_TX_EN Endpoint Enable / Direction Control
/// 0 0 Disable endpoint.
/// 0 1 Enable endpoint for TX transfer only.
/// 1 0 Enable endpoint for RX transfer only.
1 1 1 Enable endpoint for RX and TX transfers.
0 1 1 Enable endpoint for RX and TX and control (SETUP)
transfers.
Host Mode Operation
A unique feature of the USB core is its host mode logic. This logic lets devices such as digital
cameras and palmtop computers work as a USB host controller. Host mode lets a peripheral
such as a digital camera connect directly to a USB-compliant printer. Digital photos can then be
easily printed without having to upload them to a PC. Similarly, with palmtop computer
applications, a USB-compliant keyboard/mouse can connect to the palmtop computer for easy
interaction.
Host mode is designed for handheld-portable devices, allowing easy connection to simple
Human Interface Device (HID)-class devices such as printers and keyboards. It is not intended
to perform the functions of full Open Host Controller Interface (OHCI)- or Universal Host
Controller Interface (UHCI)-compatible host controllers found on PC motherboards.
Host mode allows bulk, isochronous, interrupt and control transfers. Bulk data transfers are
performed at nearly the full USB bus bandwidth. Support is provided for ISO transfers; however,
the number of ISO streams that can be practically supported depends on the interrupt latency of
the microprocessor servicing the token-done interrupts from the SIE. Custom drivers must be
written to support host mode. The USB is not supported by Windows 98 as a USB host
controller.
The USB core can operate as either a target device or in host mode. It cannot operate in both
modes simultaneously.
To enable host mode, set the HOST_MODE_EN bit in the Status register (see Status Register
on page 43). Host mode also uses the following registers:
Token Register on page 47
SOF Threshold register on page 47
During host mode, only endpoint zero is used. Software must disable all other endpoints.