Usb Special Function Registers - Renesas M16C Series User Manual

M30240 Group
1.2.18.3.3 Interrupt Endpoints
Any endpoint can be used for interrupt transfers. For normal interrupt transfers, the interrupt transactions be-
have the same as bulk transactions, i.e., no special setting is required. The IN endpoints may also be used to
communicate rate feedback information for certain types of isochronous functions. This is done by setting the
INTPT bit in the IN CSR register of the corresponding endpoint.
The following outlines the operation sequence for an IN endpoint used to communicate rate feedback infor-
mation:
1. Set MAXP > 1/2 of the endpoint's FIFO size;
2. Set INTPT bit of the IN CSR;
3. Flush the old data in the FIFO;
4. Load interrupt status information and set IN_PKT_RDY bit in the IN CSR;
5. Repeat steps 3 & 4 for all subsequent interrupt status updates.

1.2.18.4 USB Special Function Registers

The MCU controls USB operation through the use of special function registers (SFR). This section de-
scribes each USB related SFR. Some USB special function registers have a mix of read/write, read
only, and write only register bits. Additionally, the bits may be configured to allow the user to write only
a "0" or a "1" to individual bits.
• When accessing these registers, writing a "0" to a register that can only be set to a "1" by the CPU
has no effect on that register bit.
• Writing a "1" to a register that can only be set to a "0" by the CPU has not effect on that register bit.
Each figure and description of the special function registers details this operation.
All USB Special Function Registers, with the exception of USB Attach/Detach (001F
trol (000C ) must use byte access. Work access is prohibited for USB internal registers (0300
16
033C ).
16
The contents of all USB Special Functions Registers, including USB Attach/Detach and USB Control,
are preserved on a software reset.
1.2.18.4.1 USB Attach/Detach Register
The USB Attach / Detach Register is shown in Figure 1.30. The register is used to attach and detach the USB
function from a USB host without physically disconnecting the USB cable. This functionality is enabled by set-
ting P8 _Second to a "1". Doing this forces P8
3
resistor). The port driver is tri-stated and a "1" is always read from the port bit in this mode. When the ATTACH/
DETACH bit is a "1" (and P8
pulled up and the host to detect an attach. When the ATTACH/DETACH bit is a "0" (and P8
P8 is tri-stated, causing D+ to be pulled down (through the cable and 15k ohm resistor on the host/hub side)
3
and a detach to be registered by the host. A 1.5k ohm pull-up resistor must be connected externally from P8
to D+ when this functionality is used. When it is not used, the 1.5k ohm resistor should be placed between
EXTCAP and D+.
USB Attach/Detach Register
b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0 0 0
Figure 1.30: USB Attach/Detach Register
Rev.1.00 Sep 24, 2003 Page 46 of 360
to operate as a pull-up for D+ (through an external 1.5k ohm
3
_Second is a "1"), P8
3
Symbol
USBAD
Bit symbol Bit name
Port 8 -Second
P8 _2nd
3
3
Attach/
Attach/Detach
Detach
Reserved
is driven with the voltage on EXTCAP, causing D+ to be
3
Address When reset
001F 16 00 16
Function
0 : Normal mode for Port P8
3
1 : Forces Port to operate as pull up for D+.
P8
3
P8
0 : Tri-states, causing the host to detect a detach
3
1 : Drives P8 with voltage on EXTCAP , causing the host
3
to detect an attach
Must always be set to "0"
Universal Serial Bus
) and USB con-
16
-
16
_Second is a "1"),
3
3
R W