Usb Precautions - Renesas M16C Series User Manual

M30240 Group

3.2.14 USB Precautions

• When the USB Reset Interrupt Status flag is set to "1", the contents in the USB internal registers
(addresses 0300
16
affected by a USB reset:
• USB Control (address 000C
• Frequency Synthesizer Control (03DC
• USB EPx FIFO (addresses 0338
• All passive components of the LPF pin must be located as close as possible to the LPF pin.
• An insulation connector (ferrite beads) must be connected between AVss and digital Vss pins, and
between AVcc and digital AVcc pins.
• When using a DC-DC converter to supply 3.3V to the drive, connect a capacitor between the EXTCAP
pin and the Vss pin. the connection should consist of a 2.2 µ F capacitor (tantalum capacitor) and a
0.1 µ F capacitor (ceramic capacitor) connected in parallel. Use a ceramic capacitor equivalent to the
X7R type as a 0.1 µ F capacitor.
• In order to meet the USB specifications impedance requirements, connect a resistor (33 Ω ) between
the USB D+ and USB D- pins. In addition, in order to control the slew rate and rise/fall timing, connect
a capacitor (recommended: 33pF ceramic capacitor) between the USB D+ and USB D- pins or
between the USB D+/D- pins and the Vss pin. This capacitor must be connected after the resistor.
• Connect a 1.5k Ω resistor between the EXTCAP pin and the USB D+ pin during normal operation.
When using the Attach/Detach function, connect a 1.5k Ω resistor between the P8
the USB D+ pin.
• Read from/write to the USB internal registers (addresses 0300
Accessing by 16-bit mode will cause incorrect read/write values.
• When using an isochronous transfer, set the FLUSH bit as follows:
• OUT FIFO data flush: When OUT_PKT_RDY flag is "1," set the FLUSH bit to "1."
• IN FIFO data flush: Use AUTO_FLUSH bit.
• Do not write to the USB internal registers (address 0300
Suspend mode.
• Precautions for accessing the USB Interrupt Status registers 1 & 2 (USBIS1, USBIS2)
• When reading from/writing to both registers, access USBIS1 first and then USBIS2.
• When writing to these registers, use transfer instruction such as the MOV. Do not use Read Modify
Write instructions such as OR or BSET because this could cause improper values to be written back.
• Each status flag can be cleared to "0" by writing back the same value "1" which was read from the
USB Interrupt Status register. Make sure to clear only the corresponding status flag in each USB
interrupt routine. Mask the other status flags so that they are not accidentally cleared.
Rev.1.00 Sep 24, 2003 Page 326 of 360
-0335 ) will return to their reset values. However, the following register are not
16
)
16
)
16
-033C
16 16
)
-033C
16
-033C ) when the USB clock is disabled in
16 16
Universal Serial Bus
/ATTACH pin and
3
) by 8-bit mode only.
16