SN8F2270B Series
USB 2.0 Low-Speed 8-Bit Micro-Controller
9
UNIVERSAL SERIAL BUS (USB)
9.1 OVERVIEW
The USB is the answer to connectivity for the PC architecture. A fast, bi-directional interrupt pipe, low-cost, dynamically
attachable serial interface is consistent with the requirements of the PC platform of today and tomorrow. The SONIX
USB microcontrollers are optimized for human-interface computer peripherals such as a mouse, joystick, game pad.
USB Specification Compliance
— Conforms to USB specifications, Version 2.0.
— Supports 1 Low-speed USB device address.
— Supports 1 control endpoint, 3 interrupt endpoints.
— Integrated USB transceiver.
— 5V to 3.3V regulator output for D- 1.5K ohm internal resistor pull up.
9.2 USB MACHINE
The USB machine allows the microcontroller to communicate with the USB host. The hardware handles the following
USB bus activity independently of the microcontroller.
The USB machine will do:
‧ Translate the encoded received data and format the data to be transmitted on the bus.
‧ CRC checking and generation by hardware. If CRC is not correct, hardware will not send any response to USB host.
‧ Send and update the data toggle bit (Data1/0) automatically by hardware.
‧ Send appropriate ACK/NAK/STALL handshakes.
‧ SETUP, IN, or OUT Token type identification. Set the appropriate bit once a valid token is received.
‧ Place valid received data in the appropriate endpoint FIFOs.
‧ Bit stuffing/unstuffing.
‧ Address checking. Ignore the transactions not addressed to the device.
‧ Endpoint checking. Check the endpoint’s request from USB host, and set the appropriate bit of registers.
Firmware is required to handle the rest of the following tasks:
‧ Coordinate enumeration by decoding USB device requests.
‧ Fill and empty the FIFOs.
‧ Suspend/Resume coordination.
‧ Remote wake up function.
‧ Determine the right interrupt request of USB communication.
9.3 USB INTERRUPT
The USB function will accept the USB host command and generate the relative interrupts, and the program counter will
go to 0x08 vector. Firmware is required to check the USB status bit to realize what request comes from the USB host.
The USB function interrupt is generated when:
‧ The endpoint 0 is set to accept a SETUP token.
‧ The device receives an ACK handshake after a successful read transaction (IN) from the host.
‧ If the endpoint is in ACK OUT modes, an interrupt is generated when data is received.
‧ The USB host send USB suspend request to the device.
‧ USB bus reset event occurs.
‧ The USB endpoints interrupt after a USB transaction complete is on the bus.
‧ The NAK handshaking when the NAK interrupt enable.
The following examples show how to avoid the error of reading or writing the endpoint FIFOs and to do the right USB
request routine according to the flag.
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